GIFT  OF 
Mars ton  Campbell,    Jr. 


Library 


THE  STEAM  ENGINE  INDICATOR 
AND  ITS  APPLIANCES.  H;v 


BEING  A  COMPREHENSIVE  TREATISE  FOR  THE  USE  OF  CONSTRUCTING,  ERECTING 

AND  OPERATING  ENGINEERS,  SUPERINTENDENTS,  MASTER  MECHANICS, 

AND  STUDENTS,    DESCRIBING  IN   A  CLEAR  AND  CONCISE 

MANNER  THE  PRACTICAL  APPLICATION   AND  USE 

— —OF  THE 

STEAM  ENGINE  INDICATOR, 

WITH  MANY  ILLUSTRATIONS,    RULES,   TABLES,    AND   EXAMPLES  FOR  OBTAINING 

THE   BEST   RESULTS   IN   THE  ECONOMICAL   OPERATION 

OF    ALL   CLASSES  OF 

STEAM,  GAS  AND  AMMONIA  ENGINES, 

TOGETHER  WITH  ORIGINAL  AND  CORRECT  INFORMATION  ON  THE  ADJUSTMENT  OF 
VALVES  AND  VALVE  MOTION,  COMPUTING  HORSE  POWER  OF  DIAGRAMS, 
AND  EXTENDED  INSTRUCTIONS  FOR  ATTACHING  THE  INDICATOR,  ITS 
CORRECT  USE,  MANAGEMENT  AND  CARE,  DERIVED  FROM  THE  AU- 
THOR'S PRACTICAL  AND  PROFESSIONAL  EXPERIENCE,  EXTEND- 
ING OVER  MANY  YEARS,  IN  THE  CONSTRUCTION  AND 
USE  OF  THE  STEAM  ENGINE   INDICATOR. 

FOURTH  EDITION  REVISED. 

BY 

WILLIAM  HOUGHTALING. 


THE  AMERICAN  INDUSTRIAL  PUBLISHING  CO.,   PUBLISHERS, 

BRIDGEPORT,  CONN.,  U.  S.  A. 

1906. 


t* 


Engineering 
Library 

COPYRIGHT    1899 


WILLIAM  HOUGHTALING. 


ALL  INTEREST  AND  RIGHTS  RESERVED 


DEDICATION. 

To  the  young  Engineers  of  America,  who  by  thoughtful  and 
careful  study ;  are  seeking  to  make  their  opportunities  and  overcome 
obstacles  in  the  care  and  management  of  the  Steam  Engine;  this 
volume  is  respectfully  inscribed  by 

THE  AUTHOR. 


834142 


PREFACE. 

The  preparation  of  this  book  has  occupied  most  of  the  author's 
spare  time  for  a  number  of  years.  Originally  the  matter  was  not 
intended  for  publication,  but  the  manuscript  has  grown  so  large  and 
complete,  which  consideration,  combined  with  many  repeated  re- 
quests, has  induced  the  writer  to  publish  the  matter  in  book  form. 

Let  every  Engineer  make  his  own  Indicator  book  as  he  proceeds 
in  his  study  and  practice,  and  it  will  prove  invaluable  in  after  years. 
The  present  work  has  been  compiled  in  this  way,  from  data  contin- 
ually obtained  during  the  author's  professional  career,  extending  over 
a  third  of  a  century. 

The  introduction  of  algebraical  formules  have  been  avoided. 
These  are  readily  found  in  the  many  valuable  mechanical  Pocket- 
Books.  The  writer  has  endeavored  to  discuss  the  principle  and  use  of 
the  Indicator  in  as  plain  common  sense  words  as  the  subject  and  the 
English  language  will  admit  of. 

Special  attention  has  been  given  to  the  requirements  of  the  young 
progressive  student  in  Steam  Engineering.  The  preparation  of  the 
following  chapters  has  been  a  work  of  pleasure  to  the  author,  and  if 
they  prove  beneficial  to  his  fellow-workmen,  he  will  be  amply  repaid. 


.     , 


CHAPTER. 

BRIEF  HISTORY  OF  THE  INDICATOR,    -                                                ,  I. 

PURPOSE  OF  THE  INDICATOR,  II. 

DEFINITION  OF  TECHNICAL  TERMS,                                                      ~  III. 

CONSTRUCTION  OF  THE  STEAM  ENGINE  INDICATOR,   -                        -  IV. 

INDICATOR  APPLIANCES,                                                                        .  V. 

INDICATOR  APPLIANCES,  CONTINUED,                          -            -           =  VI. 

INDICATOR  REDUCING  MOTION,                                                 -            .  VII. 

DRUM  STOP  AND  ELECTRICAL  ATTACHMENT,              »••«•.  VIII. 

CARE  AND  USE  OF  INDICATOR,                         -  IX. 

To  TAKE  DIAGRAMS,    -                                                  -            „            ,   •  X. 

INDICATOR  DIAGRAMS,                                                                 ...'         -  XI. 

STUDY  OF  DIAGRAMS,  -                                                            .        .  V  XII. 

LINES  AND  POINTS  OF  THE  DIAGRAMS,                                    -           -  XIII. 

ISOTHERMAL  CURVE,                                                                  -           .  XIV. 

ADIABATIC  CURVE  AND  POINT  OF  CUT-OFF,    -  XV. 

THE  FOOT  POUND  AND  MEASUREMENT  OF  DIAGRAM,             -            -  XVI. 

EXPANSION  OF  STEAM,                                                                 -            .  XVII. 

HYPERBOLIC  LOGARITHMS.       -                                                .            .  XVIII. 

THEORY  OF  ACTION  OF  STEAM  EXPANSION  IN  CYLINDERS,    .  XIX 

READING  THE  DIAGRAMS,        -                                                  -  XX. 

DIFFERENT  METHODS  OF  COMPUTING  WATER  CONSUMPTION,            -  XXI. 

INDICATOR  TESTING  DEVICE,  -                                                -  XXII. 

PLANIMETERS,                                                    -            ...  XXIII. 

COMPARISON  DIAGRAMS  FROM  THROTTLING  AND  CUT-OFF  ENGINES,  XXIV. 

THE  ECONOMY  OF  EXPANSION,                                    .           .            _  XXV. 

THE  POINT  OF  CUT-OFF,                                               ...  XXVI. 

BACK  PRESSURE  AND  COMPRESSION,    -                        -  XXVII. 

COMBINING  THE  DIAGRAMS  FROM  COMPOUND  ENGINES,         -           -  XXVIII. 

DIAGRAMS  FROM  GAS  AND  OIL  ENGINES  AND  AMMONIA  COMPRESSORS,  XXIX. 

MAKING  CALORIMETER  TESTS,                                     -  XXX. 

MISCELLANEOUS  DIAGRAMS,     -                                    ...  XXXI. 

ENGINE  ECONOMY,        -                                                            .            .  XXXII. 

TABLES,             -                                    -                        „•„-.;,'..  XXXIII. 


CHAPTER  I. 


BRIEF   HISTORY    OF   THE    INDICATOR. 


The  idea  embodied  in  this  important  and  instructive  little 
instrument,  was  originated  by  the  celebrated  James  Watts  dur- 
ing the  latter  part  of  the  last  century,  at  a  very  early  period 
in  the  history  of  the  steam  engine,  and  it  has  since  then  in  its 
improved  forms,  materially  contributed  to  the  perfection  and 
efficiency  of  our  modern  steam  engines ,  not  only  by  enabling 
the  engineer  to  ascertain  the  exact  values  of  the  forces  from 
which  the  power  is  derived,  but  also  by  pointing  out  the  pre- 
cise periods,  in  relation  to  the  different  parts  of  the  stroke,  at 
which  these  elements  of  power  come  into  action.  The  original 
machine  of  Watts,  consisted  simply  of  a  cylinder,  about  six 
inches  long  and  one  inch  in  diameter,  in  which  there  was  a 
closely  fitted  piston;  and  was  attached  to  the  engine  cylinder 
by  means  of  a  suitable  pipe,  fitted  with  a  valve  to  open  or  close 
communication  between  them.  A  long  open  coiled  spring  was 
used,  of  which  one  end  was  fastened  to  the  piston,  and  the 
other  to  the  cover  of  the  indicator  cylinder ;  this  spring  resist- 
ed the  pressure  of  the  steam,  in  one  direction,  and  also  the 
pressure  of  the  atmosphere  in  the  other. 


12  Steam  Engine  Indicator 

A  pointer  was  connected  to  the  piston,  and  moved  directly 
with  it  and  served  to  locate  the  atmospheric  line,  or  zero ;  and 
all  motion  of  the  pointer  was  above  or  below  that  point. 
There  was  no  paper  drum ;  the  pointer  merely  indicating  on  a 
scale,  the  highest  and  lowest  pressure  in  the  engine  cylinder, 
measured  from  the  atmospheric  line.  An  improvement  on  this 
instrument  was  made  by  adding  a  flat  slide  to  which  a  sheet  of 
paper  was  secured  and  giving  it  a  coincident  motion,  on  a  re- 
duced scale,  with  the  engine  piston,  by  attaching  a  cord  from 
it  to  the  crosshead  or  some  other  moving  part  of  the  engine, 
and  returning  the  same  by  means  of  a  counterweight.  The 
machine  in  this  improved  form,  though  crude  in  comparison 
and  less  compact  in  construction,  was  almost  identical  in  prin- 
ciple of  its  operation,  to  the  many  different  instruments  now 
30  extensively  in  use,  and  it  enabled  him  to  ascertain  the  exact 
mean  effective  steam  pressure  throughout  the  stroke,  and  also 
the  proportion  which  the  vacuum  in  the  cylinder,  at  different 
parts  of  the  stroke,  bore  to  that  in  the  condenser,  in  order  to 
determine  the  dimensions  of  cylinder  required  for  any  given 
power,  as  also  the  relative  proportion  proper  to  be  given  to  the 
steam  and  exhaust  ports,  of  the  slow  speed  engines  of  his  ex- 
periments. 

Having  attained  the  objects,  he  left  for  -succeeding  engin- 
eers to  devise,  improve,  and  put  into  such  a  compact  and  por- 
table form,  as  to  be  easily  applicable  to  steam  engines  of  every 
description ;  to  such  an  extent  as  we  find  the  modern  indicator 
of  to-*day. 

One  of  the  first  to  improve  on  the  instrument  of  Watts, 
and  nearly  one-half  a  century  later,  was  Wm.  Macnaught  of 
Glasgow,  who  constructed  an  instrument  represented  at  one- 
quarter  actual  sizs  in  elevation,  Fig.  i,  and  in  plan,  Fig.  2. 

Unlike  the  indicators  of  to-day,  that  have  a  parallel  and 
multiplied  movement  of  the  pencil  as  compared  with  the  pis- 
ton ;  in  this  instrument  the  movement  of  both  are  coincident, 


'  And  Its  Appliances. 


•13 


that  is,  whatever  motion  is  imparted  to  the  piston  by  the  steam, 
the  pencil  moves  precisely  the  same  distance  either  way.  As 
constructed  in  this  way,  the  spiral  spring  op- 
posing the  force  of  the  steam  against  the  pis- 
ton, is  liable  to  disarrangement,  and  uneven- 
ness  ;  on  account  of  the  greater  length  of 
spring  necessary  to  obtain  cards  of  a  conven- 
ient height  for  computation. 

Its  consequent  general  adoption  has  led 
to  many  very  important,  and  decided  im- 
provements in  the  construction  of  the  instru- 
ment, and  very  materially  aided  in  elevating 
the  standard  of  duty  of  steam  engines,  and 
also  demonstrated  the  economy  resulting  from 
a  liberal  use  of  the  expansive  power  of  steam. 
From  a  glance  at  Figure  i ,  it  will  be  per- 
ceived that  the  Indicator  is  neither  more  nor 
less  than  a  small  single  acting  steam  engine 
with  the  addition  of  a  spiral  spring  on  the  op- 
posite side  of  the  steam  piston,  to  resist  the 
force  of  the  steam. 

The  many  treatises  at  the  present  day  on 
the  steam  engine  indicator,  leaves  little  to  be 
said  in  reference  to  the  actual  manipulation  of 
the  instrument  in  practice :  and  we  now  find 
almost  all  of  the  Stationary,  Locomotive, 
Marine,  and  other  engineers  imbued  with  the  necessity  of  un- 
derstanding the  working  of  the  indicator  in  all  its  details,  not 
only  in  the  interest  of  their  employers,  but  particularly  for 
their  own  personal  benefit,  in  acquiring  a  knowledge  of  the 
intricate  working  of  steam,  or  other  operating  forces,  of  their 
engines,  in  all  their  various  details,  and  which  becomes  neces- 
sary to  enable  them  to  reach  a  place  in  the  higher  ranks  of  en- 
gineering science. 


FIG.  2. 


14  Steam  Engine  Indicator 

The  principal  parts  of  an  indicator,  of  the  most  complete 
construction,  consists  of  an  outside  cylinder,  or  body,  inside  of 
which  is  secured  an  inner  or  working  cylinder ;  with  a  nicely 
fitting  piston,  of  exactly  one-half  of  a  square  inch  in  area, 
equal  to  about  .7978  of  an  inch  in  diameter,  working  therein. 

The  piston  is  so  closely  fitted  to  the  working  cylinder  of 
the  indicator,  that  at  the  pressures  of  from  two  to  three  hun- 
dred pounds  per  square  inch,  there  is  but  a  very  small  amount 
of  steam  that  can  pass  by  or  through  it ;  but  all  indicators  are 
subject  to  a  certain  amount  of  leakage  of  the  piston,  and  for 
which  ample  means  are  always  provided  for  its  escape ;  in  or- 
der to  avoid  any  unnecessary  back  pressure  on  the  side  of  the 
piston  opposite  the  steam  pressure. 

Where  the  indicator  is  to  be  used  for  obtaining  cards,  from 
pressures  ranging  from  four  to  six  hundred  pounds  per  square 
inch,  it  is  advisable  to  use  a  reduced  size  of  working  cylinder 
and  piston ;  the  area  of  which,  shall  only  be  one-fourth  of  a 
square  inch;  equal  to  about  .5641  of  an  inch  in  diameter,  thus 
avoiding  the  use  of  indicator  springs  of  a  very  high  tension. 
The  different  sizes  of  the  working  cylinders,  and  their  pistons, 
are  made  interchangeable  in  the  indicator,  so  that  either  can 
be  removed  at  any  time,  and  the  other  substituted. 

One  .end  of  the  piston  rod  is  connected  to  the  piston,  by  a 
ball  connected  joint,  and  the  opposite  end  to  some  part  of  a 
pencil  mechanism,  for  producing  a  so-called  parallel,  or  straight 
line  movement  of  the  pencil,  up  and  down,  in  reference  to  the 
paper  drum. 

The  parallel  motion  is  another  beautiful  and  ingenious  in- 
vention of  Watts,  as  he  applied  it  to  steam  engines,  for  the 
purpose  of  guiding  the  piston  rod,  back  and  forth  in  a  straight 
line ;  and  without  the  intervention  of  any  guides,  or  other 
means,  for  the  purpose  ;  thereby  eliminating  friction  to  a  great 
extent ;  with  smooth  working,  and  providing  a  mechanism  that 
has  since  been  used  in  various  modified  forms,  and  adapted,  to 


A  nd  Its  Appliances.  1 5 

a  certain  extent,  to  different  kinds  of  machinery  where  a  motion 
of  this  principle  is  desired. 

The  parallel  motion,  as  applied  to  his  engines,  was  consid- 
ered by  Watts,  notwithstanding  his  other  inventions,  to  be  the 
one  which  gave  him  the  greatest  satisfaction  and  pride,  as  it 
performed  its  mission  with  the  best  practical  results ;  even 
though  not  absolutely  mathematically  correct  in  some  respects. 
In  most  of  our  modern  indicators  this  principle  of  mechanism, 
for  their  pencil  movement  has  been  almost  universally  adopted 
in  its  various  and  possible  modified  forms,  and  constant  efforts 
in  this  direction  are  being  made,  with  a  view  of  eliminating 
the  slight  inaccuracies  that  are  known  to  exist  in  the  original 
parallel  motion ;  particularly  in  the  constant  varying  ratio  of 
the  movement,  that  exists  between  the  piston  and  the  extreme 
end  of  the  system  or  the  point  at  which  the  pencil  is  located. 

The  parallel  or  straight  line  movement  of  the  pencil  is 
usually  produced  by  a  system  of  levers  and  links  of  definite 
lengths,  and  pivoted  in  such  a  manner  that  by  any  movement 
of  the  system,  up  or  down,  the  end  of  the  lever  carrying  the 
pencil  is  always  expected  to  move  in  a  straight  line,  and  also 
in  some  exact  ratio  to  the  movement  of  the  indicator  piston. 


1 6  Steam  Engine  Indicator 


CHAPTER  II 


PURPOSE    OF   THE    INDICATOR. 


The  Steam  Engine  Indicator  is  an  instrument  originally 
designed  for  recording  the  varying  pressure  of  steam  in  an  en- 
gine cylinder ;  at  any,  and  all  points  during  the  revolution  of 
the  engine,  and  has  subsequently  been  applied  under  many, 
and  various  other  circumstances,  wherever  the  record,  and 
measure  of  an  irregular  pressure  has  been  desired. 

The  production  of  this  record  is  the  result  of  two  motions, 
and  is  traced  by  the  indicator  pencil  upon  paper  that  is  secured 
to  a  light  cylinder,  called  the  paper  drum. 

To  this  drum  is  imparted  a  rotary  oscillating  motion  upon 
its  axis,  at  right  angles  to  the  motion  of  the  pencil ;  such  mo- 
tion being  derived  from  the  cross  head,  or  any  part  of  the  en- 
gine having  a  movement  coincident  with  it. 

The  motion  of  the  pencil  is  produced  by  the  varying  pres- 
sures of  steam  acting  against  the  indicator  piston ;  in  opposi- 
tion to  the  strength  of  a  spring  of  known  tension.  Conse- 
quently, an  indicator  properly  attached  too,  and  communicating 
with  the  interior  of  the  cylinder  of  a  steam  engine  in  operation, 
and  the  drum  given  a  motion  (on  a  reduced  scale)  correspond- 
ing to  that  of  the  engine  piston,  will,  (on  bringing  the  pencil 
in  contact  with  the  paper  upon  the  drum,  during  its  oscilla- 
tion), trace  the  outline  of  an  irregular  figure  upon  the  paper, 
which  is  usually  known  as,  and  called  an  Indicator  Diagram, 


And  Its  Appliances.  17 

an  example  of  which  is  represented  in  Fig.  3,  C.  D.  E.  F.  B.  B. 
and  shows  the  varying  pressure  acting  against  one  side  only  of 


FIG.  3. 

the  piston,  during  a  revolution  of  the  engine ;   and  such  pres- 
sures can  be  properly  located,  and  correctly  measured. 

The  upper  line  C.  D.  E.  F.  of  the  diagram  represents  the 
force  of  the  steam  impelling  the  piston  during  its  forward 
stroke ;  while  the  back  pressure  line  B.  B.  shows  its  retardation 
on  the  return  stroke ;  the  average  height  of  each  being  meas- 
ured, (by  the  scale  of  the  spring),  from  the  atmospheric  line 
A.  A. 

The  difference  between  their  average  height,  represents 
the  Mean  Effective  Pressure,  usually  designated  the  M.  E.  P. 
of  the  diagram. 

The  atmospheric  line  A.  A,  is  also  drawn  by  the  indicator 
but  at  a  time  when  steam  communication  between  it,  and  the 
engine  cylinder  is  closed ;  and  consequently  subjecting  both 
sides  of  the  Indicator  Piston  to  atmospheric  pressure  only. 


1 8  Steam  Engine  Indicator 

To  show  the  pressure  on  the  other  side  of  the  engine  pis- 
ton, another  diagram  must  be  taken  from  the  opposite  end  of 
the  cylinder. 

In  most  calculations  of  the  diagrams,  it  becomes  desirable 
to  draw,  by  hand,  additional  lines,  from  and  by  which,  the 
actual  lines  may  be  compared. 

First,  the  straight  line  V.  V.  is  drawn  to  represent  the  ab- 
solute vacuum,  or  absence  of  all  pressure. 

Second,  the  line  V.  O.  represents  the  clearance  volume, 
and  is  drawn  at  right  angles,  (or  perpendicular),  to  the  atmos- 
pheric line. 

Third,  the  line  O.  O.  is  drawn  to  show  the  full  boiler 
pressure  in  order  that  it  may  be  seen  on  the  diagram  how  near 
that  pressure  has  been  realized. 

The  different  lines,  and  events  of  the  stroke,  as  shown  by 
the  diagram  during  a  revolution  of  the  engine,  and  the  name 
by  which  they  are  designated  will  be  noted,  and  explained  in 
a  later  chapter. 

Diagrams  taken  from  different  engines,  and  under  vary- 
ing conditions,  will  present  themselves  in  an  almost  endless 
variety,  of  forms,  depending  entirely  upon  circumstances  con- 
nected with  the  operation. 

The  earlier  forms  of  the  instrument,  (although  the  same 
in  principle),  were  crudely  constructed,  the  moving  parts  ex- 
ceedingly heavy ;  inducing  vibrations,  sufficient  to  vitiate,  and 
distort  the  diagrams ;  also  causing  more  or  less  tardiness  at 
the  different  events  of  the  stroke,  such  as  admission  of  steam, 
point  of  cut-off,  and  also  compression  ;  because  of  the  heavy 
parts  being  unable  to  respond  so  promptly  to  change  of  pres- 
sure ;  thereby  making  them  unreliable,  and^imperfect  in  their 
action,  to  an  extent  depending  upon  the  weight  of  the  pencil 
mechanism,  rapidity  of  rotative  speed,  and  also  suddenness  of 
change  of  pressure  ;  and  therefore  preventing  their  being  suc- 
cessfully adaptable,  only  to  engines  of  very  low  rotative  speeds. 


A  nd  Its  A ppliances.  1 9 

The  prevalence  of  many  high  speed  engines  in  use  at  the 
present  time,  renders  the  use  of  the  old  type  of  indicators  al- 
most useless,  and  wholly  unsuited  for  high  speed,  where  any 
reliable  results  are  expected,  as  many  details  which  gave  little 
trouble  at  low  speed,  seriously  affect  the  results  at  the  higher 
speeds. 

The  present  improved  construction  of  some  of  the  various 
modern  indicators,  in  which  perfection  is  attained  as  near  as 
can  be  expected,  consists  principally  in  superior  designs,  sim- 
plified construction,  a  better  adaptation  of  the  pencil  mechan- 
ism, also  finer  adjustment,  convenience  of  manipulation,  and 
especially  extreme  lightness  of  the  moving  parts,  thereby 
practically  eliminating  the  effects  of  inertia,  and  momentum  of 
these  parts. 

These  qualities  in  any  Indicator  are  absolutely  indispensa- 
ble in  order  to  secure  accurate  and  reliable  results  from  high 
speed  engines. 

The  information  that  may  be  derived  from  a  careful  and 
attentive  application  of  the  Indicator  to  engines  of  all  descript- 
ions, is  almost  incalculable  to  the  engineer;  because  many 
facts  are  accurately  determined  by  its  use,  that  cannot  be  ob- 
tained in  any  other  way,  with  any  great  degree  of  satisfaction 
or  correctness ;  consequently  its  use  has  enabled  the  engineer  to 
discover  many  unforseen,  and  necessarily  unknown  defects  ex- 
isting in  the  engine,  that  have  formerly  been  veiled  in  mystery, 
and  at  the  present  time,  its  value  is  so  universally  recognized, 
and  relied  upon,  that  most  manufacturers  of  high  grade  en- 
gines, make  provision  for  its  application ;  and  do  not  consider 
their  engines  complete  until  the  valves  have  been  correctly  ad- 
justed by  the  use,  and  assistance  of  the  indicator,  and  set  in 
such  manner,  as  that  the  maximum  efficiency  of  the  engine 
shall  have  been  attained. 


2O  Steam  Engine  Indicator 


CHAPTER  III. 


DEFINITIONS   OF   TECHNICAL   TERMS. 


The  many  terms,  generally  used  in  connection  with  the 
study  of  steam  engineering-,  are  all  measurable ;  each  with 
reference  to  some  established  unit,  and  by  which  they  are  clear- 
ly defined,  and  their  correctness  recognized. 

Some  of  these  are  indispensable  to  the  engineer,  a  few  of 
which  are  briefly  described,  and  explained  as  follows : 

The  Unit  of  Work  is  equal  in  amount  to  the  power  required 
to  lift  one  pound,  one  foot  high,  and  is  called  the  Foot  Pound. 

The  Unit  of  Heat,  or  Thermal  unit,  is  the  quantity  of  heat 
necessary  to  raise  the  temperature  of  one  pound  of  water,  one 
degree,  or  from  39°  to  40°  Fah. 

Also,  one  unit  of  heat  is  equal  to  772  foot  pounds  or  units 
of  work. 

The  Sensible  Heat  of  any  body,  as  Air,  Water,  or  Steam,  is 
the  heat  that  is  sensible  to  our  touch,  and  in  extent  is  as  shown, 
and  measured  by  the  thermometer. 

Latent  Heat  of  steam  is  the  quantity  of  heat,  (expressed  in 
heat  units),  required  to  vaporize  water,  that  has  previously 
been  heated  to  a  temperature  equal  to  the  resulting  steam,  of 
vaporization. 

Specific  Heat  is  the  quantity  of  heat  measured  in  thermal 
units,  necessary  to  raise  one  unit  of  weight  of  the  substance, 
through  one  degree  of  temperature. 


And  Its  Appliances.  21 

Saturated,  or  Dry  Steam,  is  steam  confined  tinder  pressure 
in  contact  with  the  water  from  which  it  is  formed,  and  contains 
just  sufficient  heat  to  maintain  the  water  in  a  state  of  steam, 
and  will  vary  in  pressure,  and  density  corresponding  to  vary- 
ing temperatures. 

When  saturated  steam  suffers  any  loss  of  heat,  a  condensa- 
tion of  some  of  the  steam  also  takes  place. 

Superheated  Steam  is  steam  containing  an  excess  of  heat. 

If  to  saturated  steam  more  heat  be  added,  its  temperature 
will  increase,  and  the  steam  is  said  to  be  superheated,  because 
its  temperature  will  be  greater  than  that  corresponding  to  satur- 
ated steam  of  the  same  pressure.  This  excess  may  be  parted 
with/ without  condensation. 

Horse  Power  (H.  P.)  is  the  standard  used  for  measuring 
the  power  of  a  steam  engine,  and  is  equal  to  lifting  33,000 
pounds  one  foot  hfgh  in  one  minute  of  time,  or  550  pounds  in 
one  second,  or  any  equivalent  thereof  in  opposition  to  the  force 
of  gravity. 

Indicated  Horse  Power,  (I.  H.  P.)  is  the  horse  power  of  an 
engine  as  computed  from  the  Indicator  Diagram. 

If  the  mean  area  of  the  piston  in  square  inches  be 
multiplied  by  the  mean  effective  pressure  in  pounds  per  square 
inch  exerted  against  it,  and  also  by  its  speed  in  feet  per  min- 
ute;  this  product  on  being  divided  by  33,000,  will  be  the 
indicated  horse  power  of  the  engine. 

Net  Horse  Power  is  the  indicated  horse  power  of  an  engine 
less  the  horse  power  which  is  consumed  in  overcoming  its  own 
friction. 

Boiler  Pressure  is  the  pressure  above  atmosphere,  or  the 
pressure  as  shown  by  a  correct  steam  gauge. 

Initial  Pressure  is  the  pressure  in  the  cylinder  acting 
against  the  piston,  at  or  near  the  commencement  of  the  stroke 
of  the  engine. 

Absolute  Pressure  is  the  pressure  of  the  steam  calculated 
from  absolute  vacuum. 


22  Steam  Engine  Indicator 

It  is  the  pressure  as  shown  by  a  steam  gauge,  with  the 
pressure  or  weight  of  the  atmosphere  added  thereto. 

Terminal  Pressure  is  the  pressure  above  the  line  of  abso- 
lute vacuum  that  would  exist  in  an  engine  cylinder,  provided 
the  release  of  the  steam  had  not  taken  place  until  the  end  of 
the  stroke  had  been  reached. 

Usually  the  release  happens  earlier,  and  in  such  case  its 
position  may  be  located  by  continuing  the  expansion  curve  by 
hand  from  any  point  of  release,  to  the  end  of  the  diagram. 

The  terminal  pressure  must  always  be  measured  from  the 
vacuum  line ;  consequently  it  is  the  absolute  terminal  pres- 
sure. 

Mean  Effective  Pressure  (M.  E.  P.)  is  the  average  of  all  the 
varying  pressures  at  different  parts  of  the  stroke,  exerted 
against  the  engine  piston  to  impel  it  forward;  less  all  the 
pressure  that  acts  on  the  opposite  side  of  the  piston  to  retard 
its  progress. 

Back  Pressure  Line,  in  a  non-condensing  engine,  represents 
the  loss  that  occurs,  from  the  retardation  of  the  escaping  steam  ; 
due  to  atmospheric  or  other  pressure 

It  is  indicated  on  the  diagram  by  its  height  above  the  at- 
mospheric line,  and  is  expressed  in  pounds  per  square  Inch. 

On  the  diagram  of  a  condensing  engine  it  is  indicated  by 
its  height  above  a  line  drawn  by  hand  to  represent  the  absolute 
or  perfect  vacuum. 

Total  Back  Pressure  is  represented  on  the  diagram  by  its 
height  above  the  line  of  Absolute  Vacuum. 

Initial  Expansion  is  the  fall  of  pressure  along  the  steam 
line;  which  often  happens  in  an  engine  cylinder,  between  ini- 
tial pressure,  and  the  point  at  cut-off. 

Compression  is  a  result  caused  by  the  action  of  the  piston 
in  compressing  into  the  clearance  space,  all  steam  remaining 
in  the. cylinder  after  the  exhaust  valve  closes. 


A  nd  Its  Appliances.  2  3 

Clearance  is  all  of  the  space  or  waste  room  between  the 
piston  at  the  end  of  its  stroke,  and  the  face  of  the  valve. 

Its  volume  or  amount  is  usually  expressed  in  its  per  cent- 
age  of  the  piston  displacement. 

Piston  Displacement  is  the  distance  passed  over  by  the 
piston  in  traversing  a  single  stroke. 

Its  volume  is  equal  to  the  area  of  the  piston  in  square 
inches,  multiplied  by  the  length  of  stroke,  in  inches,  the  pro- 
duct is  the  volume  of  displacement  in  cubic  inches. 

Wire  Drawing  is  a  term  sometimes  applied  to  the  action 
of  steam,  and  arises  in  consequence  of  very  restricted  steam 
passages,  also  dilatory  valve  motion,  thereby  reducing  more  or 
less,  the  pressure  in  the  engine  cylinders,  and  usually  consid- 
ered to  be  a  loss  in  the  matter  of  economy. 

Valve  Lap  is  the  excess  of  length  of  the  valve  at  each 
end ;  (when  at  the  middle  of  its  stroke)  over  the  extreme  outer 
edge  of  the  steam  ports ;  and  is  designed  to  serve  as  a  cut-off 
valve  within  certain  limits. 

Valve  Lead  is  the  amount  of  opening  of  the  steam  port, 
(which  is  regulated  by  the  valve)  for  the  admission  of  steam 
to  the  cylinder,  just  as  the  piston  arrives  at  the  corresponding 
extreme  end  of  the  stroke  ;  the  entering  steam  thereby  serving 
as  a  cushion  for  the  reciprocating  parts  of  the  engine. 

Water  or  Steam  Consumption  is  the  amount  of  steam  ac- 
counted for  by  the  indicator,  per  horse  power  per  hour ;  and  is 
a  measure  of  the  economy  of  the  engine. 


Steam  Engine  Indicator 


CHAPTER  IV. 


CONSTRUCTION    OF   THE   INDICATOR. 


The  principal  difference  in  the  construction  of  the  various 
indicators  on  the  market  to-day  lies  in  the  pencil  movement 
mechanism.  The  main  objects  sought  in  the  design  of  this 

mechanism  are  as  follows : 
ist,    the    nearest    possible 
approach  to   straight   line 
vertical  movement  of  pen- 
cil parallel  to  the  axis  of 
the  steam  cylinder.     2nd, 
constant    ratio    of    move- 
ment, pencil  to  piston.   3rd, 
lightness  of  moving  parts, 
thereby  reducing  the  mo- 
mentum of  these  parts  to  a 
minimum.    4th,  accessibil- 
ity of  the  parts  and  conven- 
ience in  handling  same  to 
take  diagrams. 
For  our  intent  and  purpose,  it  is  not  necessary  to  describe 
more  than  one  of  the  various  instruments  in  the  market  to-day, 
and  we  have  in  preference  to  all  others, .selected  the  well  known 
improved  new  style  Tabor  Indicator,  as  shown  in  Figs,  4,  5  and 
6  as  being  the  instrument  more  nearly  fulfilling  all  the  con- 


FIG.  5. 


And  Its  Appliances. 


ditions  and  requirements  named;  and  which  are  absolutely 
necessary  for  the  production  of  the  most  accurate  results  in 
Indicator  practice,  including  lightness  of  moving  parts ;  there- 
by reducing  momentum ;  and  also  for  ease  and  convenience  to 
the  operator  in  handling  the  instrument  while  taking  diagrams. 
In  order  that  the  particular  advantages  of  this  instru- 
ment may  be  thoroughly  understood,  it  is  necessary  that  a 

brief  description  of  its  construction, 
and  arrangement  of  parts,  should  be 
given  here. 

The  principal  and  most  impor- 
tant peculiarity  of  this  instrument 
from  all  others,  lies  in  the  method 
employed  to  communicate  a  straight 
line  motion  to  the  pencil,  and  at  the 
same  time  of  producing  an  exactly 
equal  ratio  of  movement  between 
the  piston  of  the  Indicator  and  the 
pencil ;  both  of  which  are  perfectly 
FIG.  6.  accomplished  by  means  of  a  steel 

plate,  through  which  there  is  a  slot  (as  shawn,  full  size,  in  Fig. 
7),  of  such  contour,  or  shape,  as  to  exactly  counteract  the  ten- 
dency to  a  radial  movement  of  the  pencil  bar ;  this  slotted  plate 
is  attached  in  an  upright  position  on  the  swivel  plate  of  the 
instrument,  and  upon  which  the  whole  pencil  mechanism  is 
self-contained.  The  swivel  plate  is  in  turn  secured  to  the  cyl- 
inder cover  of  the  instrument ;  said  cover  serving  as  a  center, 
upon  which  the  entire  pencil  movement  can  be  revolved  in 
either  direction,  until  it  comes  in  contact  with  the  paper  drum. 
In  order  to  make  this  slot  in  the  plate  available  for  the  pur- 
pose, a  small  stud  is  secured  on  the  pencil  bar,  upon  which 
there  is  mounted  a  hardened  steel  roller,  fitted  so  as  to  travel 
in  the  slot  from  one  extreme  to  the  other ;  and  in  doing  this, 


26 


Steam  Engine  Indicator 


the  pencil  is  caused  to  move  in  a  straight  line  up  and  down  the 
paper  drum,  in  an  exact  ratio,  throughout  any  and  all  parts  of 
the  movement,  of  exactly  five  times  the  distance  moved  by  the 
indicator  piston. 

The  radial  slot  in  the  plate  is  an  irregular  curve  and  devi- 
ates slightly  from  a  true  circle ;  the  irregularities  existing  in 
the  curve,  just  compensating  for  the  error  that  would  occur  in 
case  a  radial  link  were  substituted,  and  corresponding  in  length 
to  the  average  radius  of  the  slot ;  where  one  end  of  said  link 
is  pivoted  to  a  stationary  point  and  the  other  to  some  part  of 
the  pencil  mechanism ;  a  method  now  employed 
in  a  number  of  the  well  known  indicators  at  the 
present  time,  and  the  results  are,  that  the  lines 
made  by  the  pencil,  which  are  supposed  to  be 
straight,  are  not  so,  nor  are  the  ratios  of  piston 
and  pencil  equal. 

A  radial  link,  the  end  of  which  always 
moves  in  a  true  circle,  is  therefore  not  a  success- 
ful substitute  for  accuracy,  as  compared  with 
the  irregular  curve  in  the  slot  plate  of  the  Tabor 
Indicator,  as  said  slot  which  guides  and  con- 

Itrols  every  movement  of  the  pencil  being  so 
formed  as  to  give  the  most  accurate  results,  in 

FIG.  7.  every   position   the    pencil    bar   may   assume. 

There  is  another  plate  of  exactly  the  same  outline,  as  the 
slot  plate  (but  without  slot)  and  secured  coincident  with  it ; 
the  roll  stud  in  the  pencil  bar  projecting  far  enough  through 
it  to  make  contact  with  said  plate,  and  serves  to  receive  any 
pressure  that  may  occur  when  the  pencil  is  brought  in  contact 
with  the  paper  drum  in  the  act  of  taking  diagrams ;  and  it  also 
prevents  the  torsional  strain  that  would  otherwise  come  on  the 
center  and  back  links,  thereby  reducing  the  friction  from  this 
cause  to  a  minimum. 


O    o 
°0 


A  nd  Its  Appliances.  2  7 

These  plates  are  provided  with  a  projecting  part  on  their 
lower  ends,  which  are  drilled  and  tapped  to  provide  for  a  screw 
passing  through,  to  regulate  the  pressure  of  the  pencil  upon 
the  paper  drum,  said  screw  coming  in  contact  with  a  standard 
secured  to  the  body  of  the  instrument.  A  small  upright  pro- 
jection on  the  swivel  plate,  serves  as  a  fulcrum  for  the  lower 
end  of  the  back  link,  the  upper  end  being  connected  to  one  end 
of  the  pencil  bar. 

The  back  and  center  links  are  made  of  a  fine  grade  of  steel 
as  also  the  pencil  bar,  which  is  hardened  and  carefully  drawn 
to  a  spring  temper,  highly  polished  and  all  given  a  blue  finish. 
The  piston  rod  is  of  steel  and  made  hollow  in  order 
to  reduce  weight,  its  upper  end  is  connected  to  the  cen- 
ter link,  and  the  lower  is  made  solid  and  terminates  in 
a  ball ;  this  ball  is  provided  with  a  universal  cap  and 
socket  and  to  which,  in  turn,  the  indicator  piston  is 
attached  by  means  of  a  thumb  nut. 

The  piston  rod  is  formed  of  three  pieces ;  the  body, 
shank  and  ball ;  and  upon  the  shank  there  is  formed  a 
collar  as  shown  at  A,  Fig.  8,  full  size,  a  little  larger  in 
diameter  than  the  body,  and  serves  as  a  safety  stop  for 
the  pencil  movement,  by  coming  in  contact  with  the 
under  side  of  the  cylinder  cover  just  before  the  pencil 
bar  reaches  its  extreme  height,  thereby  preventing  any 
further  movement  of  the  piston  rod,  which  would  be 
FIG.  s.  likely  to  result  in  injury  to  the  pencil  movement  in  case 
of  breakage  of  a  spring  when  in  use,  or  by  a  mistake  of  using 
too  light  a  spring  for  the  steam  pressure. 

The  piston  is  made  very  light,  of  a  hard  bronze  metal, 
truly  turned,  grooved  on  its  periphery,  to  act  as  a  water  pack- 
ing, and  lapped  perfectly  round  and  straight  on  its  face  to  an 
exact  size. 

On  the  projecting  arm  of  the  instrument  is  secured  a  steel 
center  stud,  extending  to  the  top  of  the  paper  drum,  and  around 


28  Steam  Engine  Indicator 

which  all  moving  parts  of  the  drum  mechanism  oscillate.  The 
spring  case  has  a  threaded  hub  and  is  permanently  secured  to 
the  stud,  and  rests  directly  on  the  top  surface  of  the  arm  and 
is  secured  thereto  by  a  mit  underneath. 

A  flanged  disc,  or  pulley,  which  carries  the  paper  drum 
has  a  projecting  hub  on  both  top  and  bottom,  which  insures  a 
long  and  accurately  fitting  bearing  on  the  stud,  working  almost 
frictionless. 

There  is  a  hook  secured  to  the  bottom  hub,  which  engages 
one  end  of  a  plain  flat  spiral  spring,  while  the  other  end  of  the 
spring  connects  to  a  similar  hook  in  the  spring  case.  A  part 
formed  on  the  disc,  is  made  to  come  in  contact  with  a  stop 
secured  to  the  projecting  arm  of  the  instrument  and  serves  to 
always  locate  it  in  a  positive  position,  when  alone  under  the 
tension  of  the  spring. 

The  lower  hub  of  the  disc  rests  directly  on  the  spring  case, 
while  the  opposite  hub  is' in  contact  with  a  knurled  thumb  nut, 
screwed  and  pinned  to  the  central  stud,  just  sufficient  to  give 
a  slight  amount  of  end  motion  to  the  disc. 

This  thumb  nut  also  serves  as  a  convenient  means  of  reg- 
ulating the  tension  of  the  spring,  as  by  loosening  the  nut  that 
secures  the  spring  case  to  the  arm  of  the  instrument,  said 
thumb  nut  can  be  turned  in  either  direction  until  the  desired 
tension  is  obtained,  and  then  tightening  the  nut. 

The  lower  part  of  the  disc  is  formed  with  a  groove,  wide 
enough  to  receive  about  two  turns  of  the  cord ;  one  end  of  the 
cord  being  made  fast  to,  and  encircling  the  groove,  and  the 
other  attached  to  a  pantograph,  pendulous  lever,  or  some  sort 
of  a  reducing  gear  that  has  a  movement  generally  derived  from 
the  motion  of  the  engine  crosshead,  and  which  causes  the  disc 
to  rotate  in  one  direction ;  the  motion  in  the  opposite  direction 
is  accomplished  by  the  retraction  of  the  spring  connecting  the 
disc  with  the  spring  case,  and  its  oscillations  are  thereby  made 
coincident  with  the  movement  of  the  engine  piston. 


And  Its  Appliances. 


29 


The  drum  upon  which  the  paper  is  placed  in  taking  cards 
is  a  very  light  cylindrical  tube,  mounted  on  the  disc,  and  moves 
in  unison  with  it:  It  has  a  guide  permanently  secured  on  the 
inside,  and  which  fits  in  corresponding  recesses  in  the  disc,  in 
order  to  serve  as  a  carrier,  and  also  to  locate  it  in  its  proper 
position  in  reference  to  the  pencil  bar,  for  either  right  or  left 

hand  indicators.  The  irop  is 
closed  and  fitted  with  a  sleeve 
that  provides  a  bearing  in 
contact  with  the  central  stud, 
and  which  serves  as  a  guide 
for  it,  and  prevents  any  irreg- 
ular motion  at  that  point.  A 
clip  is  attached  for  securely 
holding  the  paper,  one  leg  of 
which  is  made  shorter  than 
the  other  to  facilitate  the 
matter  of  adjusting  the  paper 
upon  the  drum. 

One  end   of   a   plate   of 
suitable  outline,  is  shown  in 
full  size  Fig.  9,  and  called  the 
cord  guide-base,  is  secured  to 
FIG.  9.  the  under  side  of  the  arm  of 

the  instrument  by  a  nut  for  that  purpose,  and  said  plate  can 
be  turned  in  any  desired  position  parallel  to  it.  The  other  end 
supports  the  cord-guide,  which  consist  of  a  small  grooved  pul- 
ley mounted  on  a  pin  within  the  periphery  of  a  circular  disc, 
both  being  encircled  by  a  clamp  having  a  threaded  stem,  which 
projects  through  the  plate,  and  is  secured  thereto  in  any  desired 
position  by  a  small  thumb-nut,  and  the  combination  of  the 
adjustment  enables  the  cord  to  be  correctly  guided  around  the 
pulley  and  on  to  the  flanged  disc  from  any  direction. 


3O  Steam  Engine  Indicator 

The  cock  tube  is  securely  screwed  in  the  body  of  the  in- 
strument at  the  bottom,  and  the  connection  which  secures  the 
indicator  to  the  cock  is  made  with  a  single  thread,  and  secures 
correct  attachment  at  once  without  the  annoyance  of  different 
trials,  as  is  often  necessary  with  connections  made  with  two 
threads. 

The  indicator  cock  has  a  stop,  which  limits  its  range  in 
either  direction  to  full  open  or  closed,  and  also  has  holes  pro- 
vided for  the  release  of  all  steam  that  may  remain  between  the 
indicator  piston  and  cock,  after  operating.  In  taking  cards 
where  two  indicators  are  being  used,  one  on  each  end  of  the 
steam  cylinder,  the  straight  cocks  shown  in  Fig.  14,  Chapter  5, 
are  all  that  are  necessary  for  the  production  of  cards  from  each 
on  separate  sheets  but  in  the  case  of  only  one  indicator  being 
used  there  is  considerable  trouble  and  annoyance,  as  well  as 
time  lost  to  the  operator,  in  changing  the  instrument  from  one 

end  of  the  cylinder  to  the  other. 
All  this  may  be  entirely  obvi- 
ated by  the  use  of  the  three-way 
cock  shown  in  Fig.  10,  this  cock 
being  interposed  about  midway 
of  the  steam  cylinder  in  a  line 
of  pipe  connecting  the  two 
straight  cocks  at  the  ends  of  the 
.  10.  cylinder.  This  three-way  cock 

furnishes  an  easy  and  convenient  means  of  taking  cards  from 
each  end  of  the  cylinder,  and  within  a  few  seconds  of  each 
other ;  also  on  the  same  sheet  of  paper ;  and  therefore  admits 
at  once  of  a  ready  comparison  between  the  cards.  At  all  other 
times  than  applying  the  indicator,  the  cocks  near  the  cylinder 
should  be  kept  closed. 


And  Its  Appliances. 


Fig.  ii  is  a 
sectional  view  of 
the  three-way 
cock  represented 
in  Fig.  10. 

A  very  sim- 
ple and  efficient 
cord  attachment 
is  shown  in  Fig. 

FIG.  11.  12,    providing    a 

convenient  and  easy  means  of  adjusting  the  length  of  the  actu- 
ating cord  between  the  reducing  gear  and  the  indicator,  the 
hook  that  is  fastened  on  the  cord  from  indicator  connecting  in 
the  hole  at  the  end  of  the  attachment. 

Up  to  a  comparatively  recent  date  all  indica- 
tors have  been  designed  so  that  the  piston  spring 
comes  more  or  less  in  contact  with  steam  and  hot 
vapors.  This  increases  the  temperature  of  the 
spring  and  tends  to  expand  same  thereby  tending 
to  increase  the  height  of  the  diagram  more  than 
warranted  by  the  steam  pressure  alone.  To  over- 
come this  tendency  the  springs  for  the  ordinary  or 
inside  spring  type  of  indicator  are  graduated  and 
calibrated  to  give  correct  pencil  movements  when 
subjected  to  these  higher  temperatures.  The  in- 
crements of  temperature  are  variable  under  dif- 
ferent working  conditions,  and,  while  the  inside 
spring  type  of  indicator  as  shown  in  Figs.  5  and  6  will  give 
reasonably  accurate  results  with  properly  calibrated  springs, 
it  is  obvious  that  a  better  construction  would  be  to  so  locate 
the  spring  as  to  have  it  practically  free  from  all  such  disturb- 
ing influences.  The  Tabor  indicator  is  now  made  of  both  the 
inside  spring  type  as  shown  in  Figs.  5  and  6  and  of  the  outside 


FIG.  12. 


32  Steam  Engine  Indicator 

spring  type  as  shown  in  Fig.  13.     An  examination  of  this  cut, 
together  with  Fig.  13  A  will  show  that  the  spring  is  mounted 


FIG.  13. 


above  the  top  cylinder  cap  where  the  temperature  is  but  very 
little  higher  than  the  surrounding  air.     This  construction  is 


And  Its  Appliances. 


33 


desirable  for  high  pressure  steam  work  and  especially  for  gas 
engine  work  where  the  temperatures  run  very  high  tending  to 
make  the  spring  unreliable  and  to  suffer  deterioration  in  the 
inside  type  of  indicator.  It  will  also  be  noted  that  with  this 
construction  the  spring  can  be  much  more  easily 
changed  and  without  handling  any  very  hot 
parts.  It  is  not  necessary  to  disturb  the  pencil 
motion  or  allow  the  indicator  to  cool  off  in  order 
to  change  springs. 

It  will  be  noted  from  the  above  that  springs 
for  outside  and  inside  types  of  indicator  vary. 

The  general  con- 
struction of  the 
spring  is  practi- 
cally the  same  for 
both  designs  of 
indicator.  See 
Fig.  136.  Each 
spring  consists  of 
two  distinct  coils 
of  wire  balancing 
each  other,  and 
both  mounted 
with  brass  screw- 
ed ends. 

The  principal 
requisites    for    a 

F™-  13A-  reliable  and  cor- 

rect  spring  are,  that  the  wire  should  be  of  an  exact  size,  and 
coiled  on  a  special  arbor  of  such  a  size  that  will  give  the  proper 
tension  to  the  spring  for  the  different  denominations.  They 
should  be  evenly  hardened  and  temper  drawn  uniformly  all 
over,  and  in  finishing  should  be  made  perfectly  straight  and 
true,  thereby  reducing  to  a  minimum  all  the  chances  of  any 


Spring  for  Inside          Spring  for  Outside 

Spring  Style  Spring  Style 

Indicator.  Indicator. 

FIG.  13B. 


34  Steam  Engine  Indicator 

side  strain  or  buckling  of  the  spring,  which,  always  tends  to 
force  the  indicator  piston  against  one  side  of  the  cylinder, 
thereby  creating  a  friction  on  the  piston  that  will  surely  cause 
all  results  from  it  to  be  unreliable.  The  springs  of  the  Tabor 
Indicator  are  made  of  different  lengths,  according  to  the  denom- 
ination of  the  spring,  the  low  pressure  or  light  ones  being  the 
shorter,  and  from  these  continue  to  increase  in  length  until 
the  highest  pressures  have  been  reached.  The  principal  object 
in  making  the  springs  of  different  lengths  is  that  each  may 
cause  the  pencil  to  mark  the  atmospheric  line  on  the  paper 
drum  in  an  exact  position  in  reference  to  itself,  so  as  to  have 
an  ample  range  of  movement  of  the  pencil  either  above  or  be- 
low the  line  for  both  pressure  and  vacuum.  This  variation  in 
the  length  of  the  spring  obviates  the  annoyance  and  necessity 
of  adjusting  the  length  of  the  pencil  connection  to  locate  the 
position  of  the  atmospheric  line  in  cases  where  all  springs  are 
of  the  same  length,  as  in  some  makes  of  indicators. 


A  nd  Its  Applia nces .  3  5 


CHAPTER  V. 


INDICATOR   APPLIANCES. 


It  has  been  found  advisable,  in  order  to  obtain  the  best 
results  in  indicator  practice,  to  so  construct  the  instrument 
that  the  piston  shall  have  only  a  small  amount  of  motion,  and 
that  the  movement  of  the  pencil  shall  bear  a  certain  exact  ratio 
to  the  movement  of  the  piston. 

This  ratio  varies  in  different  indicators ;  in  some,  the  pencil 
has  four  times,  while  others  have  five  or  six  times  the  piston 
movement. 

This  difference  in  ratio,  as  a  general  thing  being  a  matter 
of  selection,  or  convenience,  .of  the  makers  in  the  designing  of 
their  indicators. 

One  of  the  principal  reasons  for  having  the  piston  move 
but  a  short  distance  as  compared  with  the  pencil  movement,  is 
that  a  greater  part  of  the  friction  between  the  piston  and  cylin- 
der, due  to  a  long  and  rapid  movement,  is  eliminated;  and 
consequently  the  results  obtained  from  a  short  movement  of 
the  piston  are  much  more  accurate. 

By  this  it  is  not  to  be  inferred  that  the  shorter  the  piston 
movement  the  greater  the  accuracy ;  as  there  are  circumstances 
connected  with  the  matter  that  prevent  the  realization  of  any 
theoretical  conclusions,  in  reference  to  it ;  because  the  ratio 
between  the  piston  might  be  made  so  great  that  the  slightest 
loss  motion  in  the  piston  connections  would  be  so  multiplied 
at  the  pencil  as  to  vitiate  all  efforts  to  obtain  correct  results. 


36  Steam  Engine  Indicator 

On  the  other  hand,  by  making  the  ratio  too  small  would 
tend  toward  the  original  principle ;  where  the  piston  and  pencil 
had  equal  movement ;  therefore,  the  best  compromise  between 
the  two  extremes  becomes  desirable,  and  an  experience  with 
different  proportions  seems  to  indicate  that  a  pencil  movement 
of  five  times  that  of  the  piston,  is  best  adapted  to  average  the 
imperfections  that  become  involved  in  either  a  greater  or  less 
ratio. 

An  important  requisite,  however,  in  this  respect  is,  that 
whatever  this  ratio  may  be,  is  that  the  pencil  shall  move  ex- 
actly that  many  times  the  distance  moved  by  the  piston 
throughout  its  entire  range.  This  result  has  been  perfectly 
accomplished  in  the  Tabor  Indicator  through  its  specially  de- 
signed pencil  mechanism,  which  causes  the  pencil  to  move  at 
any  and  every  part  of  its  travel  of  exactly  five  times  the  dis- 
tance moved  by  the  piston,  and  this  in  connection  with  the 
straight  line  movement  of  the  pencil,  as  well  as  the  lightness 
of  the  moving  parts  and  absence  of  friction  always  insures  the 
accuracy  of  the  diagram. 

Preparatory  to  taking  indicator  diagrams,  it  is  well  to  see 
that  the  piping  that  connects  the  engine  cylinder  with  the 
indicator  has  been  properly  done,  and  in  the  most  convenient 
position  to  enable  the  operations  to  be  performed  successfully 
and  with  the  least  amount  of  anxiety  and  trouble  to  the  opera- 
tor. The  location  of  the  indicator  will,  of  course,  depend 
somewhat  upon  the  construction  of  the  engine  to  which  it  may 
be  applied,  but  the  principal  of  its  operation  will  always  be  the 
same  in  whatever  position  it  may  be  placed. 

In  the  indicator  piping  on  the  side  of  horizontal  engine 
cylinders,  care  should  be  taken  that  the  holes  for  the  pipe  are 
drilled  outside  of  the  point  reached  by  the  extreme  travel  of 
the  engine  piston  at  each  end  of  the  cylinder.  This  precaution 
is  taken  to  insure  that  the  piston  does  not  close,  or  even  partly 
close,  communication  between  the  inside  of  the  steam  cylinder 


And  Its  Appliances. 


37 


and  indicator  piston ;  which  would  result  in  showing,  in  many 
cases,  a  late  initial  pressure  on  the  card,  and  otherwise  cause 
it,  to  a  certain  extent,  to  be  erroneous.  It  is  also  important, 
in  all  styles  of  engines,  that  these  holes  should  be  located  as 
far  from  the  steam  ports  of  the  engine  as  convenient,  as  there 
are  instances  in  which  a  close  proximity  to  said  ports  has  to 
some  extent  influenced  the  pencil  from  indicating  correctly, 
from  the  beginning  of  the  stroke  to  the  point  of  cut  off ;  this 
being  due  to  the  rapid  inflowing  of  the  steam  through  the  ports 
and  past  the  end  of  the  pipe  that  communicates  with  the  piston 
of  the  indicator ;  thereby  causing  it  to  indicate  a  lower  pressure 
than  actually  exists  in  the  steam  cylinder. 

The  pipes,  preferably  of  brass,  should  be  as  direct  as  pos- 
sible anl  without  any  unnecessary  bends,  and  in  cases  where 

the  regular  straight  indicator  cock,  shown 
in  Fig.  14,  is  used  at  the  centre,  it  is  ad- 
visable to  use  straight  way  valves  at  the 
ends  of  the  cylinder. 

There  should  be  no  appreciable  dif- 
ference in  the  mean  effective  pressure, 
shown  by  the  cards  (under  the  same  con- 
ditions), whether  the  indicator  is  located 
at  the  end  or  centre  of  the  cylinder,  that 
would  be  due  to  any  difference  in  the 
length  of  pipe,  within  the  limit  of  the 
length  of  the  cylinder.  A  close  com- 
parison of  the  card  from  the  centre  would 
only  reveal  a  slight  increase  in  the  water  consumption  per 
horse-power  over  one  taken  at  the  end,  and  which  is  entirely 
due  to  the  added  clearance  to  the  cylinder  which  would  ensue 
from  the  greater  length  of  pipe  in  use  when  the  indicator  is 
placed  at  the  centre. 

The  next  matter  of  importance  is  in  the  selection  of  the 
best  means  of  giving  the  paper  drum  an  exact  motion  coincident 


FIG. 


38  Steam  Engine  Indicator 

with  the  motion  of  the  engine  piston  and  cross  head,  on  a  suf- 
ficiently reduced  scale,  that  will  come  within  the  limits  of  its 
motion ;  this  distance  being  limited  by  the  stop  formed  on  the 
disc  (that  carries  the  drum)  for  that  purpose.  This  entire  dis- 
tance is  never  utilized  in  practice,  as  there  must  always  be  a 
certain  amount  of  allowance  at  each  end  of  its  motion,  to  guard 
against  any  accident  that  might  occur  by  coming  in  contact 
with  the  stop. 

There  are  various  devices  for  the  purpose  of  giving  motion 
to  the  paper  drum ;  an  example  of  the  most  usual  ones  being 
shown  here  in  the  illustrations,  some  of  which  are  theoretically 
correct,  while  others  are  only  an  approximation.  The  length 
of  the  card  to  be  taken,  as  well  as  its  height,  depends  some- 
what upon  the  speed  or  number  of  revolutions  the  engine  may 
be  running  per  minute. 

In  the  slow  speeds  a  long  and  high  card  may  be  taken, 
whereas  in  the  higher  speeds  a  short  and  low  diagram  is 
necessary,  in  order  to  avoid  as  much  as  possible  the  effects  of 
inertia  of  the  paper  drum,  and  also  of  the  pencil  movement. 
With  the  new  style  Tabor  Indicator,  diagrams  can  be  taken  five 
inches  long  and  two  and  a  half  inches  irt  height  if  desirable, 
but  with  the  ordinary  speeds  up  to  100,  and  from  that  to  200 
revolutions  per  minute,  a  length  of  card  of  4  inches  in  the  first 
instance,  and  3^  in  the  latter,  will  show  well  proportioned 
diagrams.  As  a  guide  in  this  matter  it  is  recommended  that 
with  speeds  up  to  300  revolutions  per  minute  the  length  of  the 
card  may  be  3^  inches;  of  400,  3  inches;  of  500,  2^  inches; 
and  of  600,  about  2  inches  long,  which  will  insure  reliable  re- 
sults. The  piston  spring  should  also  be  of  a  higher  tension 
(that  is,  a  stronger  spring),  because,  as  the  speed  is  increased, 
it  becomes  advisable  to  decrease  the  height  of  the  diagram  in 
about  the  same  proportion  as  the  length  is  shortened. 

Diagrams  taken  in  these  proportions  seldom  require  any 
change  of  tension  of  the  drum  spring  between  the  highest  and 


And  Its  Appliances. 


39 


lowest  speeds.  The  lazy  tongs  shown  at  about  ^  actual  size 
in  Fig.  1 5  is  one  of  the  appliances  frequently  used  to  obtain  the 
necessary  coincident  motion  (on  a  reduced  scale)  between  the 
paper  drum  and  cross  head,  and  which  it  accomplishes  in  an 

accurate  and  satisfactory 
manner,  provided  the 
device  is  well  made  and 
free  from  all  lost  motion 
in  its  many  pivoted  con- 
nections. It  is  usually 
pivoted  at  the  end  (B) 
by  a  stud  and  winged 
thumb-nut  to  a  block  of 
wood,  or  an  angle  iron, 
secured  to  the  floor  of 
the  engine  room  or  in 
some  other  convenient 
position,  while  the  end 
(A)  is  fitted  in  a  suitable 
piece  secured  to  the 
cross-head  of  the  engine. 
The  actuating  cord  from  the  indicator  is  attached  to  the  cord 
pin  (E)  on  the  cross  bar  (C  D) ;  said  cross  bar  may  be  moved  in 
different  positions  with  relation  to  the  centre  (B),  by  changing 
the  screws  C  and  D,  which  hold  it  in  place,  but  the  cord  pin 
(E)  must  always  be  placed  in  a  line  with  the  centres  (A)  and  (B). 
The  position  of  the  cross  bar  C  D,  in  relation  to  B,  deter- 
mines the  length  of  travel  of  the  cord  pin  E,  and  consequently 
the  length  of  the  diagram.  No  special  care  is  necessary  to 
locate  the  position  of  B,  in  reference  to  the  cross-head  of  the 
engine,  so  long  as  the  device  works  perfectly  free  throughout 
its  range.  One  of  the  principal  advantages  of  the  Lazy  Tongs 
over  some  of  the  other  forms  lies  in  its  adaptability  to  the 
various  different  conditions  so  often  found  in  indicator  practice. 


FIG.  15. 


40  Steam  Engine  Indicator 

Fig.  1 6  represents  one  way  of  attaching  it  to  an  engine, 
when  the  indicators  are  placed  on  the  side  of  the  cylinder.  In 
this  case  it  is  worked  in  a  horizontal  (or  flat)  position,  one  end 
is  supported  by  a  standard  secured  to  the  floor,  and  of  sufficient 


FIG.  16. 

height  to  just  bring  the  cord  pin  (E)  on  a  level  with  the  cord 
guide  on  the  indicator ;  consequently,  in  this  case,  the  cord  will 
run  direct  from  the  cord  pin  to  the  indicator. 

They  may  also  be  used  in  a  vertical  position  with  equally 
good  results,  where  the  end  B  is  attached  to  a  low  block  or 
bracket  secured  to  the  floor,  and  directly  below  the  engine 
cross-head.  In  this  position  it  becomes  necessary  (in  order  to 
insure  coincidence  between  the  cross-head  and  paper  drum)  to 
use  a  small  carrying  pulley,  over  which  the  cord  must  pass  from 
the  cord  pin,  E,  and  thence  to  the  indicator.  Said  pulley  may 
be  mounted  on  an  additional  suitable  block  that  will  admit  of 
its  being  placed  exactly  on  a  level  with,  and  a  short  distance 
from  the  cord  pin,  E. 

There  are  various  other  ways  of  applying  the  Lazy  Tongs, 
as  circumstances  may  require,  which  will  suggest  themselves 
to  the  engineer,  all  depending  entirely  upon  occurring  condi- 
tions. 

Proportion  of  Lazy  Tongs.  In  order  to  enable  the  engineer 
wishing  to  construct  an  accurate  device  similar  to  that  shown 
in  the  illustration,  the  following  data  will  need  to  be  carefully 
observed  to  insure  an  accurate  motion. 


Siud  //^  Appliances.  41 

The  instrument  is  constructed  principally  of  strips  of 
thoroughly  seasoned  cherry  wood  about  one  and  ^ne-eighth 
(i^)  inches  wide,  by  three-eighths  (^)  inch  in  thickness. 

The  distance  apart  of  the  outer  holes  in  the  long  strips  is 
sixteen  (16)  inches,  while  the  length  of  the  short  strips  con- 
necting their  ends  are  only  one-half  of  that,  or  eight  (8)  inches 
between  similar  holes. 

In  the  cross  bar  C.  D.  there  are  eleven  additional  holes, 
one-half  (^4)  of  an  inch  apart,  placed  equidistant  from  each 
end,  and  are  threaded  to  admit  of  the  cord  pin  E,  being  screwed 
therein  in  its  various  positions  on  the  cross  bar. 

In  one  of  each  of  the  long  and  short  strips  are  also  eleven 
threaded  holes,  one-half  (^)  inch  apart  and  exact  duplicates  of 
those  in  the  cross  bar  C.  D.  and  to  which  the  cross  bar  is  secured 
by  screws  in  any  desired  position,  as  shown  in  the  illustration. 

The  pivoted  joints  are  constructed  of  brass  tubing  about 
five-sixteenths  (5-16)  inch  outside  diameter,  by  three-sixteenths 
(3-16)  inch  inside,  and  of  sufficient  length  to  go  through  the 
joints  and  be  riveted  over  iron  washers  on  each  end. 

This  construction  also  provides  a  means  of  tightening  the 
pivots  in  case  they  become  loose  from  wear,  by  a  further  rivet- 
ing over  of  the  tubing. 

There  is  also  placed  upon  the  pivot  between  each  joint, 
two  thin  brass  separating  washers  to  prevent  the  strips  of  wood 
coming  in  contact  with  each  other  while  in  operation ;  thereby 
obviating  the  friction  that  would  otherwise  take  place. 

The  studs  A  and  B  are  shown  one-half  size  in  Fig.  17  and 
are  made  of  round  steel,  seven-sixteenths  (7-16)  of  an  inch  in 
diameter,  and  three  and  one-half  (3^)  inches  long.  In  the 
middle  of  their  length  is  secured  a  collar  three-quarters  inch  in 
diameter  and  one-quarter  of  an  inch  in  thickness.  Each  of 
these  studs  on  one  side  of  the  collar  are  made  with  nut  and 
washer,  and  serve  as  pivots  to  connect, the  ends  of  the  device. 


42 


Steam  Engine  Indicator 


The  opposite  end  of  stud  A  is  made  either  straight  or 
tapering  as  occasion  requires,  to  connect  with  the  cross-head ; 
while  the  opposite  end  of  stud  B,  is  threaded,  and  provided 
with  winged  nut,  for  the  purpose  of  attaching  to  the  fulcrum, 

or   to   whatever  the  device  may  be 
suspended ;  as  before  mentioned. 

In  order  that  the  cross  bar  may 
not  come  in  contact  with  the  nut  and 
washer  of  the  stud  B,  when  the  de- 
vice is  closed,  the  bar  is  elevated  by 
means  of  two  wooden  washers,  one 
FIG.  17.  at  each  end,  made  of  the  same  mate- 

rial as  the  strips,  and  the  screws  for  securing  the  same  are  of 
sufficient  length  to  reach  through  both,  and  screw  into  the 
drilled  strips  underneath. 

It  is  exceedingly  important  that  all  corresponding  holes  in 
the  strips  be  layed  out  and  drilled  with  extreme  accuracy,  and 
also  the  pivots  made  a  close  fit  therein,  to  insure  its  perfect 
working  at  all  points,  from  its  closure  to  the  full  extension. 

In  this  construction  of  the  Lazy  Tongs,  the  location  of  the 
holes,  their  distance  between  centres,  and  the  position  of  the 
cross  bar  in  relation  to  the  stud  B,  determines  the  ratio  (that 
occurs  in  each  case)  in  the  amount  of  motion  of  the  cord  pin  E, 
as  compared  with  the  amount  of  motion  of  the  stud  A. 

The  holes  being  one-half  inch  apart,  a  change  of  the  cross 
bar  from  one  hole  to  the  next,  results  in  a  change  of  motion  of 
the  cord  pin  E,  of  one-forty-eighth. 

For  instance ;  If  the  cross  bar  be  secured  in  the  holes  that 
will  bring  it  nearest  to  the  stud  B,  and  if  the  cord  pin  E,  there 
be  placed  in  the  hole  that  comes  in  line  between  the  studs  A 
and  B,  the  reduction  of  motion  of  the  cord  pin  will  be  three- 
forty-eighths,  or  one-sixteenth  of  that  of  the  stud  A;  in  the 
second  hole  the  reduction  is  four-forty-eighths,  or  one-twelfth ; 
in  the  third  hole,  it  is  five-forty-eighths;  in  the  fourth  hole 


And  Its  Appliances.  43 

it  is  six-forty-eighths,  or  one-eighth  and  so  on,  to  the  farthest 
holes  from  B,  where  the  motion  of  the  cord  pin  becomes  thir- 
teen-forty-eighths  of  that  of  the  stud  A. 

From  this  it  will  be  seen  that  each  position  of  the  cross  bar 
has  its  own  ratio  of  movement  between  the  cord  pin,  and  stud 
A,  as  above,  whatever  the  length  of  stroke  of  the  engine  may 
be. 

In  every  position  of  the  cross  bar  C.  D.  (if  made  according 
to  directions),  there  is  always  one  of  its  holes  on  an  exact  line 
between  the  centres  of  the  studs  A  and  B,  and  into  which  the 
cord-pin  E,  must  always  be  placed  in  order  that  it  may  move  in 
an  exact  straight  line  parallel  to  the  motion  of  the  stud  A. 


* 


44 


Steam  Engine  Indicator 


CHAPTER  VI, 


INDICATOR   APPLIANCES    CONTINUED. 


An  accurate  and  simple  form  of  pantagraph  is  shown  in 
Fig.  1 8,  in  which  the  end,  A,  is  connected  with  the  engine 

cross-head  by  means  of  a 
pin  or  other  suitable  con- 
nection ;  while  the  end,  B, 
is  pivoted  to  a  bracket,  C  ; 
said  bracket  also  serving- 
as  a  support  for  the  guide 
pulley,  E,  and  upon  which 
it  may  be  adjusted  at  a 
level  to  coincide  with  the 

cord  Pin'  D- 

The  length  of  travel  of 
the  cord  pin  depends  en- 
tirely  upon  the  distance 
the  cross-bar,  F,  may  be 
placed  in  relation  to  the  fulcrum,  B.  There  is  a  slot  in  this 
cross  bar  which  admits  of  an  adjustment,  and  the  securing  of 
the  cord  pin,  D,  in  any  required  position  within  the  length  of 
the  slot ;  and  in  whatever  position  the  cross  bar  may  be  placed, 
the  cord  pin  must  always  be  moved  and  secured  by  means  of 
the  thumb  nut,  on  a  line  between  the  points  A  and  B  in  order 
to  insure  an  exact  straight  movement  of  the  pin,  D,  and  paral- 
lel with  the  engine  cross-head. 


And  Its  Appliances. 


45 


This  instrument,  like  the  Lazy  Tongs,  may  be  used  in 
either  a  horizontal  or  vertical  position  ;  it  has  a  less  number  of 
pivoted  connections  and  accomplishes  equal  accuracy ;  but  has 
not  quite  the  same  range  of  application  under  all  circumstances. 
In  all  cases  and  with  either  instrument,  where  they  are  placed 
in  a  position  requiring  the  use  of  a  carrying  pulley,  care  must 
be  taken  that  said  pulley,  E,  be  located  a  short  distance  from 
the  instrument,  and  in  such  position  that  the  actuating  cord 
will  move  parallel  with  A,  from  the  cord  pin,  D,  to  the  pulley, 
E,  and  thence  in  any  desired  direction  to  the  Indicator. 


FIG.  19. 

Fig.  19  represents  the  pantagraph  in  its  application  to  an 
engine  cylinder,  where  the  indicators  are  placed  upon  the  side 
of  the  cylinder.  In  this  case  blocks  of  wood  or  iron  is  shown, 
secured  to  the  floor,  to  serve  as  supports  for  the  instrument,  as 
well  as  the  carrying  pulleys;  this  arrangement  answers  the 
purpose,  but  the  bracket,  C,  in  Fig.  18,  is  much  more  me- 
chanical. 

A  simple  method  of  obtaining  the  drum  motion,  and  very 
frequently  used  by  engineers  (in  the  absence  of  a  more  accurate 
device),  is  the  pendulous  lever,  A  B,  shown  in  Fig.  20,  which 
consists  of  a  strip  of  wood,  about  4  inches  wide,  by  fa  inches 
thick,  and  suspended  from  a  bracket,  G,  which  is  secured  to 
the  ceiling  or  any  overhead  framing ;  the  lever  being  of  suffi- 
cient length  from  its  point  of  suspension,  so  that  its  lower  end, 


Steam  Engine  Indicator 


A,  may  connect  to  one  end  of  the  connecting  bar,  C,  while  the 
opposite  end  of  said  bar  is  attached  to  the  engine  cross-head, 
^  D.  The  length  of  the  lever,  A  B, 

should  be  such  that  the  end,  A, 
should  be  as  far  below  the  line  of 
movement  of  the  cross-head,  when 
on  its  center  of  travel,  as  it  will 
be  above  the  line  at  its  extreme 
end  of  stroke. 

The  cord  pin,  E,  (to  which  one 
end  of  the  indicator  cord  is  at- 
tached), is  located  at  such  a  dis- 
tance from  the  point  of  suspen- 
sion, B,  as  will  rotate  the  paper 
drum,  an  amount  that  will  give  the 
FIG.  20.  desired  length  of  the  diagram. 

In  this  device  it  is  necessary  to  pass  the  cord  from  the  pin,  E, 
over  the  guide  pulley,  F,  and  thence  ^ 

to  the  indicator.      In   connecting  the  — 
device,  it  is  important  that  the  cross- 
head,   D,  should   be   at  its   center   of 
travel,   when  the  lever,   A  B,  is  in  a 
vertical  position. 

This  reducing  motion  may  be  easily 
and  cheaply  constructed  and  set  up  by 
any  engineer,  and  will  be  found  a  con- 
venient means  of  giving  motion  to  the 
paper  drum ;  but  although  not  mathe- 
matically correct,  will  give  fair  results. 

Fig.  21  shows  another  device,  the 
same  in  principle,  but  instead  of  the 
cord  pin  there  is  substituted  a  segment  FIG.  21. 

of  a  circle,  having  its  center  at  B,  and  with  a  radius  necessary 
to  give  the  paper  drum  the  desired  amount  of  motion. 


And  Its  Appliances. 


47 


In  place  of  the  connection,  C,  as  in  Fig.  20,  the  lower  end 
of  the  lever  at  A  is  slotted  and  is  worked  by  a  stud,  secured  to 
the  engine  cross-head,  D.  Whenever  this  device  can  be  placed 
in  a  direct  line  with  the  indicator,  the  guide  pulley  can  be  dis- 
pensed with,  and  the  cord  encircling  the  segment  may  be  run 
from  it  directly  to  the  indicator. 

As  the  relative  length  of  the  lever  in  this  arrangement  is 
constantly  changing  throughout  its  stroke,  it  is  therefore  as  to 
the  matter  of  inaccuracy  about  equal  to  Fig.  20. 

The  plan  of  suspended  lever,  shown  in  Fig.  22,  is  an  im- 
provement on  the  previous  ones  shown,  and  was  proposed  by 

1__ ^r*   Frank  Richards  in 

an  article  published  in 
the  American  Machinist 
several  years  ago,  in 
which  he  gives  a  number 
of  modifications  of  the 
same  principle,  whereby 
perfect  theoretical  ac- 
curacy is  attained.  It 
consists  of  an  ordinary 
suspended  lever,  with 
the  lower  end,  A,  slotted 
and  driven  by  a  pin  se- 
cured to  the  engine  cross- 
head  ;  the  end,  B,  being 
""FIG.  22.  pivoted  to  the  bracket, 

G,  which  may  be  secured  to  the  ceiling  or  some  suitable  frame 
work  (or  it  may  be  used  in  a  horizontal  position  if  desired) ; 
the  other  element  of  the  lever  at  C  also  being  slotted,  and  giv- 
ing motion  to  a  sliding  bar,  F,  by  means  of  a  pin  fastened  to 
said  bar,  and  working  freely  in  the  slot  in  the  lever.  The  bar, 

F,  slides  in  hangers  secured  in  the  same  manner  as  the  bracket, 

G,  and  in  a  line  parallel  to  the  line  of  the  cross-head.       The 


48  Steam  Engine  Indicator 

cord,  attached  to  the  sliding  bar,  passing  in  a  line  over  a  suita- 
ble guide  pulley  and  thence  to  the  indicator.  By  this  arrange- 
ment the  relative  length  of  the  elements  of  the  lever,  A  B,  al- 
ways remains  the  same,  and  consequently  insures  coincidence 
and  accuracy  of  the  drum  movement,  throughout  its  entire 
range. 

The  various  different  modifications  of  this  principle,  to  at- 
tain accuracy  of  the  drum  motion,  depends  upon  the  use  of  the 
sliding  bar,  F,  in  each  instance,  and  it  is  evident,  as  well  as 
readily  seen,  that  it  makes  no  difference  (so  far  as  accuracy  is 
concerned),  whether  the  lever,  A  B,  is  slotted,  or  instead  of  the 
slots,  we  substitute  two  permanent  pins  in  the  lever,  and  have 
each  pin  work  in  slots  formed  in  both  sliding  bar,  F,  and  in  a 
suitable  slotted  piece  secured  to  the  engine  cross-head. 

Figs.  20,  21,  and  22  show  the  position  of  the  lever,  A  B, 
when  engine  cross-head  is  at  the  center  of  its  stroke.  In  order 
to  determine  the  proper  distance  (of  the  point  on  the  lever  to 
which  the  cord  is  attached),  from  the  fulcrum,  B,  to  take  any 
desired  length  of  card,  it  is  necessary  first  to  divide  the  stroke 
of  the  engine  cross-head,  in  inches,  by  the  desired  length  of 
the  card  required ;  then  divide  the  total  length  from  center  to 
center  of  the  lever,  A  B,  by  that  quotient,  which  will  give  the 
distance  of  the  point  in  inches  from  the  fulcrum,  B,  to  the  pin, 
E,  or  where  the  cord  must  be  attached.  For  example,  sup- 
pose the  stroke  of  the  cross-head  to  be  24  inches,  the  length  of 
the  lever,  A  B,  between  centres  to  be  48  inches ;  and  we  desire 
to  produce  an  indicator  card  4  inches  long ;  then  24  inches  di- 
vided by  4  inches,  the  length  of  the  desired  card,  is  equal  to  6, 
and  by  dividing  the  length  of  the  lever,  A  B,  which  is  48 
inches  by  6,  gives  us  8  inches,  which  is  the  proper  distance 
from  the  fulcrum,  B,  to  a  point  on  the  lever  to  which  the  cord 
must  be  attached  to  produce  a  card  4  inches  in  length. 

A  slight  discrepancy  will  sometimes  appear  in  the  length 
of  cards,  computed  from  any  rules,  owing  to  incorrect  meas- 
urements, stretching  of  the  cord,  inertia  of  the  paper  drum,  &c. 


A  nd  Its  Appliances. 


49 


Fig.  23  shows  another  modification  of  the  lever  and  slid- 
x*  ing  bar,   F,   in  which  the 

slots  in  the  lever  have  been 
dispensed  with,  the  lever 
being  attached  to  the  cross- 


(g!r\head  and  bar  F  by  means 
of  the  connections  A  H 
and  C  E.  An  important 
matter  in  this  construction 
is  that  the  lengths  of  the 
two  connecting  links  must 
bear  the  same  ratio  to  each 
_  other,  as  the  ratio  between 
the  two  elements  of  the 
lever,  A  B  and  B  C ;  there- 
fore AB:BC::AH:CE.  The  pins  on  the  cross-head  and  the 
sliding  bar  must  be  so  located  that  lines  drawn  through  the 
centres  of  the  connections  A  H  and  C  E,  will  be  parallel  with 
each  other  in  any  position 
the  lever  may  assume.  In 
the  arrangement  shown  in 
Fig.  24  the  fulcrum  of  the 
lever  is  at  the  pin,  C,  of 
the  sliding  bar,  F,  while 
the  ends  are  each  made  in 
the  form  of  a  fork,  the  end, 

A,  being   moved   by   and 
sliding  upon  a  pin  secured 
to  the  cross-head,  the  end, 

B,  moving  on  a  pin  fasten-  FlG-  24- 

ed  to  the  bracket,  G.      In   Figs.  23  and  24  the  cross-head  is 
represented  at  the  extreme  end  of  the  stroke. 


50  Steam  Engine  Indicator 

These  are  modifications  of  Fig.  22,  but  without  claiming 
any  particular  advantage  for  one  over  the  other.  In  all  cases 
where  this  principle  is  accurately  applied,  it  will  be  found  that 
the  elements  of  the  lever,  A  B,  are  always  in  a  line  at  a  right 
angle  to  the  line  of  movement  of  the  engine  cross-head,  at  the 
time  the  cross-head  is  at  the  centre  of  its  travel. 

The  sliding  bar  principle  may  also  be  well  adapted  to  en- 
gines where  the  end  of  the  engine  shaft  is  accessible.  By  in- 
serting a  stud,  A,  in  the  end  of  the  shaft,  as  shown  in  Fig.  25, 
at  a  proper  distance  from  the  centre,  C,  to  give  the  desired 
length  of  card,  and  connecting  it  to  a  sliding  bar,  F,  by  means 

of  a  short  connection, 
A  B,  will  insure  a  per- 
fect coincident  motion 
of  the  engine  cross-head 


4- 


FIG-  25.  on  a  reduced  scale.     The 

bar  may  be  extended  to  any  desired  length  to  secure  conven- 
ience in  connecting  with  the  indicator.  A  necessary  requisite, 
to  insure  correctness  by  this  arrangement,  is  that  the  length  of 
the  connection,  A  B,  relative  to  the  distance  of  the  end,  A, 
from  the  centre,  C,  must  bear  the  same  proportion  that  the 
main  crank  of  the  engine  bears  to  its  own  connecting  rod.  It 
is  not  necessary  in  this  case  that  the  slide  move  parallel  with 
the  movement  of  the  cross-head,  as  it  may  be  moved  in  any  desir- 
ed direction,  but  great  care  must  be  taken  that  stud  A  be  placed 
in  such  position  on  the  shaft  that  the  sliding  bar,  F,  will  be  on 
its  extreme  throw  at  the  same  exact  time  that  the  engine  crank 
is  at  its  extreme  movement,  and  both  at  the  same  end  of  the 
stroke.  Where  the  end  of  the  shaft  is  not  accessable,  the  same 
results  may  be  accomplished  by  means  of  an  eccentric  placed 
in  a  convenient  position  on  the  shaft. 

A  reducing  arrangement,  that  gives  good  results  at  high 
speeds,  is  a  plain  lever  swinging  on  a  pin  above  (or  it  may  be 
below)  the  cross-head,  having  a  pin  in  the  end  which  slides  up 


A  nd  Its  Appliances.  5 1 

and  down  in  a  slotted  piece  of  metal  fastened  to  the  cross-head 
as  shown  in  Fig.  26.  This  method  gives  a  fairly  accurate 
motion.  A  segment  of  a  grooved  pulley  is  fastened  to  the 


FIG.  26. 

upper  end  of  the  lever,  and  from  this  the  cord  extends  to  the 
indicator. 

The  whole  device  should  be  made  of  wood  as  light  as  pos- 
sible, (consistent  with  strength),  in  order  to  reduce  the  inertia 
to  a  minimum.  A  heavy  reducing  gear  on  a  high  speed  engine 
will  wear  very  quickly  and  create  inaccuracies  in  the  diagram. 

When  indicating  High  Speed  Engines  or  Locomotives,  the 
driving  cord  for  hooking  on  the  indicator  should  be  continued 
beyond  the  loop,  and  fastened  to  a  spring  or  an  elastic  band 
attached  to  the  carrier  pulley  of  the  indicator. 

This  band  or  spring  is  intended  to  always  keep  a  tension 
on  the  driving  cord,  whether  the  indicator  is  in  operation  or 
not,  and  prevents  entanglement  and  breakage  of  cord  when 
the  indicator  is  unhooked. 

The  cut  in  Fig.  27  shows  the  arrangement  as  described, 
and  which  operates  in  a  perfect  satisfactory  manner,  as  dia- 
grams can  be  taken  with  as  little  difficulty  at  high  speeds,  as 
on  slow  speed  engines. 


52  Steam  Engine  Indicator 

The  hook,  A,  on  the  indicator  cord  connects  into  the  loop, 
B,  on  the  driving  cord  when  the  indicator  drum  is  in  operation ; 


FIG.  27. 

the  loop,  B,  is  made  long  enough  to  be  held  with  the  hand 
when  hooking  on  the  indicator. 

To  disconnect,  merely  catch  the  hook  and  hold  it  station- 
ary for  a  second,  and  the  loop  will  come  off.  The  rubber  band 
then  takes  the  motion  and  keeps  the  cord  taut. 

Whatever  arrangement  is  employed,  it  is  desirable  to  avoid 
the  use  of  long  stretches  of  cord  on  account  of  its  sagging  and 
stretching.  Small  wire  may  be  used  to  good  advantage  on 
vertical  lengths  except  where  the  line  passes  over  pulleys. 

Whatever  the  style  of  reducing  motion  that  may  be  em- 
ployed for  giving  motion  to  the  indicator  drum,  its  accuracy 
can  easily  be  tested,  and  ascertained  in  the  following  manner: 
Lay  off  a  number  of  points  on  the  cross-head  guides,  at  say  l/& , 
VM  ^8,  }4,  YQ  in.  etc.,  of  the  stroke. 

Connect  the  Indicator  with  the  reducing  motion  in  the 
same  manner  as  for  taking  diagrams.  When  the  cross-head 


A  nd  Its  Appliances. 


53 


is  on  either  dead  centre,  bring  the  pencil  in  contact  with  the 
paper  on  the  drum  and  make  a  short  vertical  line. 

In  the  same  manner  make  other  lines  on  the  paper,  as  the 
cross-head  is  moved  to  each  successive  eighth  point  on  the 
guide. 

Then  if  the  lines  on  the  paper  are  exactly  at  eighths,  the 
motion  of  the  cross-head  has  been  accurately  reduced. 

These  directions  given  for  reducing  motions  are  general ; 
some  special  cases  require  special  modifications. 


54 


Steam  Engine  Indicator 


CHAPTER  VII. 


INDICATOR   REDUCING   MOTION. 


There  are  a  number  of  devices  tinder  different  names,  all 
designed  for  the  purpose  of  giving  the  necessary  accurate  mo- 
tion to  the  paper  drum; 
and  each  constructed  on 
principles  in  which  long 
swinging  levers  are  dis- 
pensed with,  the  actuating 
cord  from  these  devices 
being  connected  either 
directly  to  the  engine  cross- 
head,  or  to  some  moving 
t>art  that  has  a  motion  in 

JL 

exact  unison  with  it ;  while 
another  and  separate  cord 
connects  the  device   with 
the   indicator.     If,   in  the 
act  of  operating  the  indi- 
cator  with    any   of    these 
'devices,  it  becomes  desir- 
ous of  stopping  the   mo- 
28.  tion  of  the  paper  drum,  it 

is  necessary  to  disengage, 

or  unhook,  either  one  or  the  other  of  the  cords  that  give  it  mo- 
tion ;    a  matter  with    some    of   them,    requiring   considerable 


And  Its  Appliances. 


55 


FIG.  29. 


practice  to  accomplish  with  ease  and  assurance  especially  on 
engine  having  high  rotative  speed.  This  operation  of  unhook- 
ing is  usually  performed  on  the  cord  connecting  the  device 
with  the  Indicator.  Some  of  these  attachments  are  constructed 
so  as  to  be  attached  to  the  indicator  by  means  of  a  bracket, 

adapted  to  the  particular 
indicator  to  which  it  is  to 
be  applied ;  while  others 
are  so  made,  that  may  be 
secured  away  from  the  in- 
dicator, to  some  part  of  the 
cylinder  or  engine  framing 
by  means  of  set  screws  or 
bolts ;  in  many  cases  re- 
quiring considerable  labor 
to  secure  them  in  a  con- 
venient position. 
The  particular  Reducing  Gear,  of  which  we  shall  give  a 
description  in  this  article,  is  one  that  is  constructed  with  and 
forms  a  complete  part  of  the  well  known  Tabor  Indicator, 
as  illustrated  in  Fig.  28.  After  securing  the  indicator 
in  position  on  the  pipe  connecting  with  the  engine  cylinder, 
and  attaching  the  end  of  the  actuating  cord  to  a  stud 
screwed  in  the  cross-head,  the  instrument  may  be  used  during 
the  time  of  any  experiment,  without  the  necessity  of  connect- 
ing and  disconnecting  the  actuating  cord,  in  order  to  start  or 
stop  the  motion  of  the  per  drum. 

The  principal  parts  of  this  Reducing  Gear  consists  of  sup- 
porting base  K,  Fig.  29,  with  two  short  standards,  B,  and  B1. 
The  standard  B1  is  fitted  with  a  hardened  steel  center  P,  Fig. 
30,  which  serves  as  a  pivot  bearing  for  the  end  of  the  worm 
shaft  R,  Fig.  3 1 ,  and  which  receives  the  entire  thrust  of  the 
shaft  R,  thus  reducing  the  friction  from  that  factor  to  a  mini- 
mum ;  the  other  bearing  being  in  the  standard  B.  The  base 


Steam  Engine  Indicator 


FIG.  30. 


K  is  connected  direct  to  the  Indicator,    upon  the  projecting 
arm    that  supports  the   paper  drum   B,   and  the  teeth  of  the 
worm  shaft,  R,  engage  directly  with  the  teeth  on  the  drum  car- 
rier g,  thereby 
making  a  posi- 
tive     connec- 
tion therewith, 
^nd  forming  a 
part  .of  the  In- 
dicator,    (see 
FIG.  81.          Fig.28).  Tothe 
base  K,  is  also 

connected  the  spring  case  D,  Fig.  32,  permanently  secured 
thereto,  by  means  of  screws  passing  through  holes  as  shown  in 
the  spring  case,  and  corresponding  with  holes  tapped  into  the 
standard  B,  (as  shown)  of  base  K,  and  so  located  thereon  that 
its  centre  shall  be  common  with  the  center  of  the  worm  shaft  R. 

Upon  the  worm  shaft  R,  is  secured 
by  means  of  a  set  screw,  the  collar  A, 
through  which  freely  slides  the  clutch 
pin  I,  one  end  of  which  is  securely  fas- 
tened to  the  thumb  piece  U,  by  which  the 
pin  is  operated.  The  whole  mechanism 
of  that  part  is  shown  complete  in  Fig.  33. 
The  flanged  pulley  O,  Fig.  34,  rotates  FIG.  32. 

freely  and  independently  forward  and  back  on  the  worm  shaft 
R.  It  has  its  outer  hub  formed  in  the  shape  of 
a  double  cam  clutch,  with  steel  pins  X,  X,  in- 
serted to  prevent  wear  upon  their  faces,  while 
the  opposite  side  has  a  hole  in  which  the  pin  A, 
of  the  spring  case  cover  S,  Fig.  35  engages. 
One  end  of  the  actuating  cord  is  attached  to  the 
pulley  O,  (a  hole  being  shown  in  the  figure  for  that  purpose) 
while  the  other  is  secured  either  to  the  engine  cross-head ;  a 


FIG. 


And  Its  Appliances. 


57 


FIG.  34. 


standard  bolted  to  the  same,  or  to  any  other  part  that  has  an 
exact  similar  movement,  and  should  be  connected  from  the 
pulley  O,  in  a  line  parallel  to  the  movement  of  the  cross-head. 
The  length  of  the  actuating1  cord  should  be  such,  that  when 
connected  to  the  cross-head,  at  the  commencement  of  the  outward 
stroke  of  the  engine,  there  should  also  be 
about  six  or  seven  turns  of  the  cord  encir- 
cling the  pulley  O,  which  will  always  in- 
sure the  requisite  amount  of  cord,  and  ob- 
viate the  liability  of  breaking. 

Enclosed  in  the  spring  case  D,  Fig.  32, 
(not  shown  in  the  illustration)  is  a  small  plain 
Spiral  Spring ;  one  end  of  which  is  secured 
to  the  spring  case  by  means  of  a  slot  F,  shown  in  the  figure, 
while  the  other  end  connects  with  the  hook  C  of  the  spring 
case  cover  S,  Fig  35.  This  spring  operates  to  return  the  pul- 
ley O,  back  to  its  starting  point,  after  it  has  been  revolved  in 
one  direction,  by  the  outward  movement  of  the  engine  cross- 
head  ;  therefore  as  this  pulley  O,  has  an  independent  rotating 
forward  and  back  motion  on  the  worm  shaft,  R,  the  necessity 
of  unhooking  the  cord  in  order  to  stop  the  motion  of  the  paper 
drum  B,  after  the  diagram  has  been  taken,  will  be  entirely 
overcome,  as  explained  further  on. 

The  paper  drum  B,  is  rotated  forward 
by  means  of  the  pulley  O,  through  the 
worm  shaft  R,  engaging  with  the  teeth  of 
the  gear  g,  on  the  drum  carrier ;  and  in  the 
opposite  direction  by  the  action  of  its  own 
retracting  spring.  On  the  top  of  the  drum  B,  is  a  knurled 
thumb-piece,  with  a  projecting  pin  on  its  under  side,  for  the 
purpose  of  engaging  with  a  similar  pin,  secured  in  the  top  of 
the  drum,  and  is  to  be  used  by  the  operator  when  in  the  act  of 
starting  the  drum ;  for  the  purpose  of  moving  it  slightly  for- 
ward before  the  clutch  pin  I,  is  pushed  in  engagement  with 


FIG.  35. 


58  Steam  Engine  Indicator 

the  cam  hub  of  the  pulley  O,  thereby  preventing  the  drum 
carrier  from  striking  against  its  stop  on  the  return  motion. 

With  this  reducing  gear  the  stopping  of  the  drum  motion 
becomes  a  very  simple  matter,  and  is  accomplished  by  taking 
hold  of  the  thumb  piece  U,  and  withdrawing  the  engagement 
between  the  clutch  pin  I  and  the  clutch  hub  of  the  pulley  O. 

The  knurled  thumb  piece  on  the  top  of  drum  B,  also  fur- 
nishes another  very  convenient  (and  preferable)  means  of  stop- 
ping the  motion  of  the  drum ;  as  by  holding  it  so  as  to  retard 
the  motion  of  the  drum  on  its  return  stroke,  it  will  thereby 
cause  the  cam  face  of  the  pulley  O,  (which  is  constantly  in  mo- 
tion) to  automatically  force  the  clutch  pin  I  out  of  contact  with 
the  clutch  hub  of  the  pulley  O.  The  starting  or  stopping  of 
the  paper  drum,  at  any  time,  will  have  no  effect  on  the  motion 
of  the  pulley  O,  which  will  continue  to  revolve  independently 
while  the  engine  is  in  motion.  When  desirous  of  starting  the 
drum  B,  it  will  be  necessary  to  again  make  the  engagement  be- 
tween the  clutch  pin  I  and  the  clutch  hub  of  the  pulley  O,  and 
which  must  be  done  by  the  combined  means  of  the  thumb 
piece  U,  and  the  thumb  piece  on  top  of  drum  B,  as  follows : 
The  pulley  O,  being  in  constant  motion ;  with  one  hand  take 
hold  of  the  thumb  piece  on  top  of  drum'B,  and  turn  it  in  a 
direction  from  right  to  left,  until  it  carries  the  drum  and  its 
carrier  a  short  distance  from  its  stop,  (say  about  J^  inch). 
While  holding  the  drum  in  this  position,  take  hold  of  the 
thumb  piece  U,  with  the  other  hand  and  gently  press  it  toward 
the  clutch  hub  of  the  pulley  O,  and  it  will  be  found  that  when 
the  engine  cross-head  arrives  at  its  extreme  inner  stroke,  that 
the  engagement  between  the  clutch  pin  I  and  the  clutch  hub  of 
pulley  O  will  ahvays  take  place  at  that  particular  point,  and 
with  the  least  amount  of  difficulty  in  the  operation. 

The  thumb  pieces  are  so  constructed  that  they  may  be 
readily  held  in  the  hand  while  running ;  therefore  no  difficulty 
is"  experienced  in  throwing  the  clutch  pin  in  or  out  of  gear.  In 


And  Its  Appliances.  59 

preparing  to  use  this  Reducing  Gear,  the  first  and  very  im- 
portant matter  for  consideration  is  in  the  selection  of  the  pul- 
ley O,  which  shall  be  of  such  size  in  relation  to  the  stroke  of 
the  engine  as  will  give  the  requisite  length  of  the  Indicator 
Diagram. 

A  ready  and  mental  means  of  ascertaining  this,  is  by  divid- 
ing the  length  of  the  stroke  of  engine  (in  inches),  by  twelve, 
which  will  give  the  diameter  (in  inches),  of  the  pulley  O,  that 
is,  the  stroke  of  the  engine  being  12  inches  will  require  the 
pulley  O  to  be  one  inch  in  diameter ;  a  stroke  of  1 8  inches,  i  y2 
inch ;  of  24  inches,  2  inch ;  and  of  36  inches  a  pulley  of  3 
inches  in  diameter,  &c. ;  and  it  is  also  well  in  this  connection 
to  bear  in  mind  that  for  each  complete  revolution  of  the  worm 
shaft  R,  there  will  a  corresponding  pencil  line  (when  in  con- 
tact), marked  on  the  paper  drum  horizontally,  about  one  inch  in 
length  ;  consequently,  two  revolutions  mark  two  inches ;  three 
revolutions  gives  three  inches,  length  of  card,  &c. 

It  must  be  understood  that  this  calculation  of  the  size  of 
pulley  O,  has  reference  to  engines  having  low  rotative  speed, 
say  up  to  1 20  revolution  per  minute,  and  where  a  long  card  is 
desired;  but  when  the  speed  is  increased  from  this  to  500  or 
600  revolutions  per  minute,  the  size  of  the  pulley  O  will  have 
to  be  in  accordance  with  the  recommendation  (in  chapter  V) 
in  reference  to  the  height  and  length  of  diagram  advisable, 
where  the  rotative  speeds  are  gradually  increased  up  to  600 
revolutions  per  minute,  and  producing  a  card  two  inches  in 
length. 

After  selecting  the  pulley  required,  remove  the  clutch  from 
the  worm  shaft  R,  by  slacking  the  set  screw  shown  in  collar  A, 
and  place  the  pulley  thereon,  taking  care  that  the  pin-hole  on 
the  inner  side  of  the  pulley  (not  shown  in  cut),  engages  with 
the  projecting  pin  A,  of  the  spring  case  cover  S,  Fig.  35,  then 
replace  the  clutch  on  the  shaft  as  far  as  it  will  go  and  secure  it 
firmly  in  place  by  the  set  screw  in  collar  A. 


60  Steam  Engine  Indicator 

Place  the  indicator  in  position,  and  attach  the  actuating 
cord  as  already  described. 

The  tension  of  the  spring  in  the  spring  case  D,  must  be 
sufficient  at  all  times  to  just  keep  the  cord  taut,  and  this  may 
be  regulated  by  taking  more  or  less  extra  turns  of  the  cord 
around  the  pulley  O,  until  it  results  in  the  desired  tension. 
The  alignment  of  the  Indicator,  in  order  to  have  the  cord  run 
evenly,  is  a  matter  to  be  observed ;  and  if  upon  starting  the 
engine  the  cord  should  run  unevenly  on  the  pulley  O,  it  may 
be  entirely  remedied  by  slacking  the  indicator  connection  a 
trifle,  and  turning  the  Indicator  slightly  in  the  necessary  direc- 
tion until  a  perfect  and  uniform  winding  of  the  cord  is  ob- 
tained, and  which  can  (by  this  means)  always  be  accomplished. 

The  peculiar  construction  of  the  angular  teeth  on  the  worm 
shaft  R,  and  also  on  the  drum  carrier  G,  enables  each  to  be- 
come the  driver  of  the  other ;  that  is,  on  the  outward  stroke  of 
the  engine,  the  drum  carrier  is  driven  by  the  worm  shaft; 
while  on  the  return  or  inward  stroke,  the  worm  shaft  is  driven' 
by  the  drum  carrier  g,  through  the  action  of  its  retracting 
spring ;  said  spring  always  serving  to  return  both  of  them  back 
to  their  normal  positions,  at  the  extreme  inner  stroke  of  the 
cross-head,  at  each  revolution  while  in  operation. 

In  the  absence  of  a  proper  understanding  of  the  principles 
of  manipulating  some  of  the  various  Reducing  Motions  in  the 
market,  some  engineers  that  have  had  no  particular  experience 
with  them,  look  upon  all  such  devices  as  complicated  and  gener- 
ally troublesome  to  operate  and  are  satisfied  to  continue  the 
use  of  the  more  antiquated  pantagraph  and  lever 'movements. 

In  our  own  experience  and  that  of  engineers  who  have 
been  using  the  positive  Reducing  Gear,  described  and  illus- 
trated in  this  article,  it  may  be  said  to  have  given  entire  satis- 
faction in  all  cases,  and  a  return  to  any  of  the  old  methods, 
(after  becoming  familiar  with  this)  could  not  be  contem- 
plated under  any  circumstances. 


And  Its  Appliances. 


61 


CHAPTER  VIII. 


DRUM    STOP    MOTION   AND    ELECTRICAL  APPLIANCE. 


In  using  the  different  lever  and  pantagraph  devices,  that 
have  been  illustrated  in  a  previous  chapter  (or  any  modifications 
of  them),  for  the  purpose  of  giving  motion  to  the  paper  drum ; 
it  becomes  necessary  with  any  and  all  of  them  to  connect  and 
disconnect  the  actuating  cord  leading  from  the  device  to  the 

indicator,  in  order  to  start  or 
stop  the  paper  drum  whenever 
necessary,  for  either  adjusting 
or  the  removal  of  the  paper 
from  the  drum.  In  slow  speed 
engines,  the  matter  of  hooking 
and  unhooking  the  actuating 
cord  is  of  no  great  difficulty; 


FIG.  36. 

but  with  engines  of  high  rotative  speed,  it  becomes  more  diffi- 
cult and  requires  much  more  skill  and  experience  on  the  part 
of  the  operator  to  perform  the  operation  successfully  and  with 


62  Steam  Engine  Indicator 

ease.  An  efficient  and  very  simple  attachment,  which  may  be 
adapted  to  different  styles  of  indicators,  for  the  purpose  of 
starting  and  stopping  the  paper  drum  at  all  times  without  the 
necessity  of  unhooking  the  actuating  cord,  when  used  in  con- 
nection with  any  of  the  pantagraph  styles  of  reducing  motion, 
is  illustrated  in  Fig.  36,  attached  in  this  case  to  a  Tabor  Indi- 
cator ;  and  whereby  the  usual  handling  of  the  actuating  cord 
(that  otherwise  becomes  necessary),  to  stop  the  motion  of  the 
paper  drum,  is  entirely  obviated  at  any  and  all  speeds. 

The  device  is  shown  in  Fig.  37  detached  from  the  indica- 
tor, and  consists  of  an 
arm  A,  which  may  be 
secured  to  a  part  X  of 
the  indicator,  by  means 
of  the  set  screw  B.  Up- 
FIG.  37.  on  the  arm  A,  Fig.  37, 

is  a  slide  C,  which  may  be  adjusted  to  any  desired  position  on 
the  arm  and  secured  thereto  by  the  knurled  nut  E  and  washer 
F.  On  the  slide  C  is  mounted  the  cord  pulley  D  for  the  pur- 
pose of  directing  the  actuating  cord  (from  any  form  of  reduc- 
ing motion),  around  the  said  pulley  and  thence  on  to  the  paper 
drum  carrier  to  the  indicator. 

The  method  of  determining  the  proper  length  of  the  actu- 
ating cord. is  as  follows:  set  the  slide  C,  to  its  extreme  inner 
position  on  the  arm  A,  and  place  the  engine  on  its  extreme 
outer  stroke,  then  bring  the  cord  from  the  drum  carrier  around 
the  cord  pulley  D,  and  thence  in  the  required  direction  to  the 
point  of  attachment  on  the  reducing  motion,  which  will  give 
the  necessary  length  of  the  actuating  cord.  At  any  convenient 
position  on  the  actuating  cord  and  near  the  cord  pulley  D, 
there  is  superposed  an  elastic  band,  shown  in  Fig.  36,  for  the 
purpose  of  taking  care  of  the  slack  of  the  cord,  that  will  appear 
when  the  engine  is  in  motion  and  the  paper  drum  at  rest. 
This  slack  is  owing  to  the  length  of  the  actuating  cord  being 


And  Its  Appliances.  63 

taken  when  the  engine  is  at  its  extreme  outer  stroke ;  conse- 
quently on  its  arrival  at  the  inner  stroke  there  is  an  amount  of 
cord  to  be  taken  care  of,  equal  to  the  presumed  length  of  the 
indicator  diagram,  and  the  intervention  of  the  elastic  band  is 
for  that  purpose  only. 

While  the  slide  C  is  at  its  inner  position  no  motion  will  be 
transmitted  to  the  paper  drum ;  but  by  moving  the  slide  C  out- 
ward upon  the  arm  A,  it  will  at  once  cause  the  paper  drum  to 
rotate  forward  and  back,  and  the  slide  may  be  secured  in  any 
desired  position  on  the  arm  by  means  of  the  knurled  nut  E, 
therefore  in  order  to  start,  or  stop  the  motion  of  the  paper 
drum  at  any  time  when  the  engine  is  in  motion,  it  is  only  nec- 
essary to  change  the  position  of  the  slide  C  on  the  arm  A, 
which  is  accomplished  most  satisfactorily,  by  means  of  the 
knurled  nut  E. 

To  start  the  paper  drum,  move  the  slide  outward  on  the 
arm  and  secure  it  by  the  nut  E,  and  to  stop,  move  it  to  its  ex- 
treme inner  position,  the  actuating  cord  continuing  its  usual 
motion  during  the  time  the  engine  is  in  motion. 

To  Take  Diagrams  Simultaneously.  In  order  to  make  com- 
plete and  reliable  tests  of  steam  power  from  the  various  com- 
pound and  multiple  cylinder  engines,  or  whenever  it  is  desirous 
to  take  diagrams  simultaneously  from  a  number  of  steam  cylin- 
ders (in  which  as  many  indicators  are  used),  it  becomes  neces- 
sary to  provide  some  sure  means  of  operating  the  indicators, 
by  which  an  operator  can  accomplish  the  object  alone,  without 
the  aid  of  assistants  and  with  the  certainty  that  all  diagrams 
taken  at  any  particular  stroke  of  the  engine  or  engines,  will 
all  commence  and  leave  off  simultaneously  with  each  other,  and 
thereby  dispensing  otherwise  with  the  number  of  attendants 
necessary  to  operate  the  different  indicators  at  some  decided 
upon  signal ;  a  plan  whereby  an  exact  coincidence  of  the  dia- 
gram at  any  particular  stroke  is  very  rarely  obtained  owing  to 
the  almost  impossible  concerted  action  between  the  operators. 


64  Steam  Engine  Indicator 

The  taking  of  diagrams  from  two  or  more  cylinders  at  the 
same  exact  stroke  of  the  engine  or  engines,  may  be  accom- 
plished successfully  in  different  ways  that  will  oft-times,  as  oc- 
casion requires,  suggest  themselves  to  the  engineer.  An  ar- 
rangement sometimes  used  with  fair  success,  consists  of  a  small 
reservoir  of  compressed  air  from  which  the  pressure  is  com- 
municated to  a  small  piston  within  a  cylinder  secured  to  each 
indicator ;  one  end  of  the  piston  rod  being  in  contact  with  some 
part  of  the  pencil  mechanism,  consequently  any  movement  of 
the  piston  is  communicated  directly  to  the  said  mechanism, 
which  results  in  a  contact  (when  under  pressure  from  the  reser- 
voir), between  the  pencil  and  paper  drum ;  and  a  withdrawal 
of  the  pencil,  (through  the  action  of  a  spring)  when  the  pres- 
sure is  released.  These  small  cylinders  are  connected  to  the 
reservoir  by  means  of  rubber  tubing  in  which  there  is  a  cock 
for  admitting  and  releasing  the  air  pressure  upon  the  piston. 
The  operation  of  the  device  being  about  as  follows :  after  seeing 
that  the  parts  are  properly  connected,  start  the  pencil  mechan- 
ism of  the  indicators  in  motion,  by  opening  the  cock  connected 
to  each,  then  by  opening  the  cock  from  the  reservoir  the  pres- 
sure from  that  source  (through  the  small  piston  and  its  rod), 
will  force  the  pencil  in  contact  with  the  paper  drum  and  against 
the  resistance  of  the  spring.  The  time  of  contact  between  the 
pencil  and  paper  drum  is  supposed  to  be  during  one  complete 
revolution  of  the  engine,  unless  an  average  card  is  desired  from 
a  number  of  revolutions.  The  instantaneous  release  of  the  air 
pressure  against  the  small  pistons,  takes  place  in  the  act  of 
closing  the  cock  ;  it  being  provided  with  an  escape  hole  for  that 
purpose,  thereby  admitting  of  the  spring  to  at  once  move  the 
pencil  out  of  contact  with  the  paper  drum. 

In  the  absence  of  a  reservoir  of  compressed  air,  the  same 
results  may  be  obtained  in  this  device,  by  using  a  jet  of  steam 
through  a  small  pipe  leading  from  the  boiler,  steam  pipe,  or  from 
any  convenient  place  where  a  pressure  of  steam  may  be 


And  Its  Appliances. 


obtained.  Other  improvised  means  depending  upon  circumstan- 
ces and  the  ingenuity  of  the  engineer,  may  be  used  to  produce 
the  desired  result.  The  most  successful,  simple,  and  satisfactory 

results,  may  however,  be  ob- 
tained by  the  use  of  the 
electric  current.  A  very  neat 
and  simple  electrical  attach- 
ment to  enable  an  operator 
to  produce  diagrams,  from 
any  number  of  cylinders  dur- 
ing the  same  stroke  of  the 
engine  by  simply  pressing  a 
button  to  close  the  electrical 
circuit  is  represented  in  Fig. 
38,  as  attached  (in  connection 
with  the  reducing  motion), 
to  the  well  known  Tabor  In- 
dicator. 

The  attachment  consists  of 
a  specially  constructed  mag- 
net M,  mounted  on  and  secured  to  a  support  S,  which  encircles 
the  body  of  the  indicator,  and  is  held  in  position  by  the  clamp- 
ing screw  E.  Also  secured  to  the  support  are  the  binding 
screws  C  and  the  spring  D, 
these  parts  being  shown  sepa- 
rate from  the  indicator  in  Fig. 

39- 

The  stud  B,  Fig.  40,  is  screw- 
ed   into    the    upright    on    the 
swivel   plate   that    carries    the 
pencil  mechanism  of  the  indi- 
cator and  serves  as  a  support  FIG.   39. 
for  the  armature  A,  Fig.  41,  and  to  which  it  is  secured  by  a 
small  set  screw  for  that  purpose ;  therefore  any  movement  of 


FIG. 


66  Steam  Engine  Indicator 

the  armature  A,  in  either  direction,  relative  to  the  magnet  M, 
produces  a  similar  motion  of  the  pencil  (in  the  opposite  direct- 
ion), to  or  from  the  paper  drum  of  the  indi- 
cator. 

The  spring  D,  Fig.  39,  is  formed  so  as  to 
hold  the  armature  within  the  field  of  the  mag- 
net, before  the  current  is  established,  and  also 
to  quickly  release  it  when  the  'current  from  •FlG<  41< 
the  battery  is  broken.  The  magnet  M,  consists  of  a 
FlG-  40-  single  spool  of  soft  iron,  wound  in  the  usual  manner  with 
insulated  magnet  wire,  and  enclosed  by  a  soft  iron  shell,  the 
combination  thereof  establishing  the  two  poles  of  the  magnet, 
when  subjected  to  the  effect  of  an  electric  current  passing 
through  the  wire.  The  armature  A  is  also  constructed  of  a 
soft  grade  of  iron  and  is  finished  to  a  diameter  the  same  as  the 
magnet  shell,  and  is  adjustable  on  the  stud  B,  to  exactly  coin- 
cide with  the  magnet  M.  On  the  side  facing  the  magnet  are 
two  small  brass  pins  for  the  purpose  of  assisting  in  the  instan- 
taneous release  of  the  armature,  from  the  magnet  after  the  cur- 
rent is  broken.  This  electrical  device  is  easily  attached  or  de- 
tached in  a  few  seconds,  and  its  connection  with  the  indicator, 
does  not  in  any  way  interfere  with  the  usual  manipulations  of  the 
operator,  in  adjusting  the  paper  to,  or  removing  it  from  the 
paper  drum ;  changing  of  the  springs  in  the  instrument,  or  any 
minor  operations  that  may  become  necessary,  as  the  pencil 
mechanism  is  free  to  be  revolved  in  any  convenient  position. 

It  is  represented  in  Fig.  38,  as  being  attached  to  a  Right- 
hand  Indicator,  but  it  may  be  used  on  a  Left-hand  instrument 
with  equal  facility.  The  change  from  one  to  the  other  is  easily 
and  readily  made  in  the  following  manner :  first  unscrew  the 
cap  (that  carries  the  pencil  mechanism),  and  take  it  complete 
from  the  indicator,  then  by  loosening  the  clamping  screw  E, 
the  support  S  may  be  readily  removed,  and  it  only  remains  to 
unscrew  the  magnet  M,  from  the  support  S,  and  change  the 


And  Its  Appliances.  67 

location  to  directly  the  opposite  side  of  the  support  and  secure 
it  in  that  position,  by  means  of  the  small  screws  for  that  pur- 
pose. The  binding  screws,  as  well  as  the  spring  D,  will  also 
need  reversing  on  the  support  S ;  the  parts  all  being  provided 
with  means  by  which  it  may  (if  necessary)  be  easily  and  readily 
accomplished.  Replace  the  device  on  the  indicator  in  a  re- 
versed position  and  secure  it  by  the  clamping  screw  E.  Where 
the  circuit  is  short  the  device  may  be  operated  in  connection 
with  a  single  indicator,  by  any  one  of  the  well  known  batteries 
in  the  market,  (either  dry  or  liquid). 

In  our  own  experience,  and  in  all  cases  where  such  an  ap- 
pliance is  desired,  and  where  accuracy  is  necessary,  this  simple 
electrical  device  seems  to  meet  all  requirements,  being  easily 
attached  or  detached,  without  any  change  in  the  mechanism  of 
the  indicator ;  instantaneous  in  its  action,  and  can  b'e  relied  up- 
on at  all  times  to  give  correct  results,  with  the  least  amount  of 
labor  and  anxiety  to  the  operator. 


68  Steam  Engine  Indicator 


CHAPTER  IX. 


CARE  AND  USE  OF  INDICATOR. 


Before  attaching  the  indicator,  open  the  cock  and  allow 
steam  to  blow  through  the  pipes  for  the  purpose  of  removing 
any  scale  or  dirt  that  may  remain  in  the  pipe  after  fitting  up  ; 
as  it  is  of  the  greatest  importance  that  all  parts  of  the  indicator 
be  kept  in  good  working  order,  where  a  close  degree  of  accu- 
racy is  expected.  The  most  important  of  these  parts,  are  the 
cylinder  and  piston;  to  which  especial  attention  should  be 
directed  as  to  their  condition ;  because  the  accumulation  of  de- 
posit, or  dirt  of  any  description  between  their  surfaces  of  con- 
tact, (however  minute)  will  produce  irregularities,  and  distor- 
tions in  the  diagram,  to  such  an  extent,  as  will  render  it  almost 
impossibe  to  secure  the  information  a  diagram  is  intended  to 
convey ;  therefore  it  becomes  very  essential  at  frequent  intervals 
to  remove  the  piston  from  the  cylinder ;  (which  can  be  done  by 
simply  unscrewing  the  cap  upon  which  the  whole  mechanism 
is  attached,  and  lifting  from  the  instrument)  and  thoroughly 
clean  both,  by  the  use  of  cotton  cloth,  waste,  or  some  other 
suitable  material. 

This  being  accomplished,  lubricate  these  parts  with  some 
good  cylinder  oil,  and  replace  them  again  in  the  instrument. 

'The  pivots  or  joints  of  the  pencil  movement,  should  also 
be  kept  clean,  and  oiled  occasionally  with  some  light  machine  oil 


And  Its  Appliances.  69 

that  will  not  gum  or  become  sticky ;  a  bottle  of  which  usually 
accompanies  the  instruments  of  all  makers. 

This  should  be  used  sparingly  as  a  very  small  amount 
suffices  for  the  purpose,  and  any  surplus  should  be  cleaned  off. 

It  is  absolutely  necessary  that  there  be  perfect  freedom  in 
•the  pencil  mechanism ;  (and  when  not  subject  to  the  action  of  a 
spring)  the  pencil  bar  on  being  raised  to  its  highest  position, 
should  from  its  own  weight,  fall  with  the  utmost  freedom  to 
its  lowest  position,  and  this  requirement  is  very  essential  in 
order  to  insure  correct  diagrams.  A  further  test  of  its  correct- 
ness may  also  be  made  by  again  raising  the  pencil  bar  to  its 
extreme  height,  and  covering  (with  the  thumb  or  finger)  the 
hole  through  which  the  steam  is  admitted  against  the  indicator 
piston  ;  and  if  the  mechanism  be  not  impeded  in  any  way,  ex- 
cept only  by  the  air  contained  within  the  indicator  cylinder, 
the  pencil  will  descend  slowly  and  uniformly  until  it  reaches 
its  lowest  position.  Should  this  be  found  otherwise  than  as 
stated,  it  may  become  necessary  to  disconnect  the  parts  of  the 
movements  from  the  piston,  and  test  each  part  separately  until 
the  cause  of  the  trouble  is  located. 

The  Paper  Drum  also  requires  attention,  it  being  in 
constant  motion,  and  subject  to  considerable  wear;  conse- 
quently should  be  examined  from  time  to  time,  and  the 
bearing  cleaned,  and  thoroughly  lubricated,  using  the  same 
light  machine  oil,  as  for  the  pencil  movement. 

With  the  ordinary  paper  on  the  drum  the  Siberian  lead 
pencil  about  grade  H.  H.  H.  H.  should  be  used  in  taking  the 
diagrams ;  the  pencil  being  sharpened  to  a  fine  round  point 
with  a  knife  or  fine  file. 

A  more  satisfactory  result  of  the  tracings  may  be  obtained 
by  the  use  of  a  chemically  prepared  paper,  (called  metallic 
paper),  upon  the  drum,  and  using  a  point  made  of  common 
brass,  or  preferably  silver  wire  suitably  sharpened  for  the  trac- 
ing point. 


70  Steam  Engine  Indicator 

One  sharpening  of  the  metallic  pencil  will  give  good  re- 
sults on  a  large  number  of  diagrams,  and  the  general  character 
of  the  work  will  be  much  more  satisfactory  than  with  the  lead 
pencil.  The  paper  should  be  placed  upon  the  drum  in  such  a 
manner  that  it  will  be  perfectly  smooth.  This  may  best  be 
done  by  first  folding  one  end,  and  slipping  it  under  the  longer 
clip ;  then  pass  the  paper  around  the  drum  and  bring  the  loose 
end  under  the  short  clip ;  taking  the  two  ends  thus  located, 
between  the  thumb  and  finger,  and  with  the  other  hand  by  a 
slight  pressure  at  the  top  of  the  card,  slide  the  whole  down  the 
drum ;  the  outer  edge  may  then  be  folded  back  over  the  clip  if 
needed. 

Adjust  the  stop  screw  so  that  the  pencil  will  bear  lightly 
on  the  paper,  otherwise  the  friction  between  the  pencil  and 
card  will  cause  the  diagram  to  be  irregular,  and  will  not  repre- 
sent the  true  action  of  the  steam  within  the  cylinder. 

Paper  Drum  Motion.  The  motion  of  the  paper  drum  may 
be  derived  from  various  different  parts  of  the  engine,  but  what- 
ever point  is  selected,  it  is  essential  that  the  motion  of  the 
drum  shall  coincide  in  miniature,  exactly  with  that  of  the  en- 
gine piston,  at  every  part  of  the  stroke. 

Owing  to  the  irregular  motion  of  the  engine  piston,  dur- 
ing the  stroke,  caused  by  the  varying  angularity  of  the  con- 
necting rod,  it  is  often  uncertain,  and  difficult  to  select  a  point 
(other  than  the  engine  cross-head),  that  shall  fulfill  the  exact 
conditions  required  ;  but  if  such  other  point  should  be  chosen, 
careful  attention  as  to  its  location  becomes  necessary,  in  order 
that  the  motion  resulting  therefrom,  may  in  no  wise  vitiate 
the  diagram. 

The  Cross- Head  being  directly  connected  to  the  piston 
rod,  consequently  moves  at  every  part  of  the  stroke,  and 
under  all  circumstances  in  exact  unison  with  the  engine  piston  ; 
therefore,  it  is  the  part  usually  selected  from  which  to  obtain 
the  motion  of  the  drum ;  as  being  the  most  direct,  reliable,  and 


And  Its  Appliances.  71 

convenient  for  the  purpose ;  but  the  amount  of  its  movement, 
(whatever  that  may  be),  must  be  reduced  to  suit  the  range  of 
the  paper  drum,  or  the  length  of  the  diagram  to  be  taken ;  and 
this  reduction  must  be  in  an  exact  proportion,  throughout  the 
stroke,  to  the  movement  of  the  cross-head. 

Where  special  reducing  wheels  are  used  for  this  purpose, 
a  stud  is  generally  screwed  in  the  cross-head,  of  sufficient 
length,  such  as  will  cause  the  cord  from  the  reducing  wheel, 
when  attached,  to  be  in  a  direct  and  parallel  line  with  its 
motion. 

It  often  happens  that  this  plan  cannot  always  be  successfully 
accomplished,  owing  to  the  various  different  construction  of 
engines ;  hence  in  such  cases  a  resort  to  the  use  of  small  carry- 
ing pulleys  will  be  necessary. 

Carrying  Pulleys.  It  is  always  desirable  to  avoid  these  pul- 
leys wherever  possible,  as  their  use  are  often  detrimental ;  in 
that  they  increase  the  tension  on  the  cord ;  cause  the  cord  to 
become  dirty  from  the  oil  used  in  lubricating  the  pulley; 
which  will  in  a  short  time  render  it  unfit  for  further  use ;  they 
also  create  a  friction  that  becomes  an  additional 
tax  upon  the  drum  spring,  and  in  many  ways 
becomes  a  source  of  annoyance  to  the  opera- 
tor. 

Nevertheless  occasions  often  occur,  where 
their  use  becomes  indispensable,  and  in  such 
cases  they  should  be  located  at  such  points,  as 
will  suggest  themselves  to  the  ingenuity  of  the 
engineer,  as  best,  for  obtaining  the  desired  re- 
sults. The  style  shown  in  Fig.  42  is  universal 
and  meets  all  requirements. 

Various  devices,  and  methods  for  reducing 
FIG"  42.  the  amount  of  movement  of  the  engine  cross- 
head  to  any  desired  length  of  diagram,  will  be  found  repre- 
sented aud  described  in  Chapters  5,  6  and  7. 


72  Steam  Engine  Indicator 

The  Indicator  Cord.  The  usual  manner  of  imparting  mo- 
tion from  the  engine  cross-head  to  the  drum,  is  through  the 
medium  of  a  hard  braided  linen  cord ;  and  sometimes  a  metal- 
lic cord  (such  as  fine  piano  wire),  may  be  used  to  advantage  in 
connection  with  it,  under  circumstances  where  an  unusual 
length  of  cord  is  required. 

Cord  of  all  kinds  especially  when  new,  is  possessed  of  a 
certain  amount  of  elasticity,  of  which  it  becomes  necessary  to  re- 
move as  near  as  possible,  before  using,  in  order  to  avoid  any 
further  stretch  when  in  use ;  so  that  coincidence  of  motion  be- 
tween the  cross-head,  and  the  reduced  motion  of  the  paper 
drum  shall  be  practically  uniform. 

The  most  simple  and  ready  method,  and  the  plan  usually 
adopted  for  removing  this  elasticity  is  by  suspending  the  cord 
from  one  end,  and  attaching  sufficient  weights  to  the  other ; 
allowing  it  to  remain  so  suspended  from  12  to  24  hours;  or  un- 
til it  becomes  apparent  that  any  further  stretching  may  result 
in  injury  to  the  cord. 

The  cord  that  is  intended  especially  for  indicator  work  is 
usually  stretched  by  the  manufacturers  until  its  elasticity  is 
eliminated,  and  therefore  will  not  stretch,  when  in  use  under 
ordinary  circumstances,  to  any  extent  that  would  seriously  in- 
terfere with  the  accuracy  of  the  diagrams. 

A  simple,  light,  and  exceedingly  convenient  cord  adjust- 
er is  represented  in  Fig.  12,  Chapter  IV,  for  adjusting  the 
length  of  the  cord  between  the  indicator  and  reducing  gear. 

The  hook  on  the  cord  from  the  indicator,  should  be  at- 
tached as  close  to  the  indicator  as  possible ;  (to  prevent  any 
swaying  of  the  cord),  and  connect  into  the  ring  of  the  cord  ad- 
juster, while  the  small  holes  in  the  adjuster  receive  the  cord 
from  wherever  the  motion  is  derived. 

The  Indicator  Spring.  The  denomination  of  the  spring  to  be 
used  in  any  particular  case,  depends  principally  upon  the  boil- 
er pressure.  A  book  usually  accompanies  most  indicators, 


And  Its  Appliances.  73 

which  gives  the  necessary  information,  (either  by  a  table  di- 
rect, or  by  a  computation  rule),  for  the  selection  of  the  most 
suitable  denomination  of  spring,  for  any  given  boiler  pressure. 

In  indicators  which  have  a  range  of  pencil  movement  of 
from  2^/2  to  3  inches  in  height,  a  40  pound  spring  is  a  good 
standard  for  pressures  between  80  and  90  pounds,  and  a  50 
pound  spring  for  boiler  pressures  from  100  to  120  pounds  per 
square  inch.  Each  indicator  spring  is  numbered  to  correspond 
with  the  pressure  per  square  inch  required  to  compress  it  an 
extent,  sufficient  to  cause  a  vertical  movement  of  the  pencil  of 
exactly  one  inch. 

For  example:  In  case  a  50  spring,  as  shown  in  Fig.  13, 
Chapter  IV,  is  used,  a  pressure  of  50  pounds  per  square  inch 
in  the  engine  cylinder,  will  raise  the  pencil  one  inch,  or  a 
pressure  of  one  pound  will  raise  the  pencil  -fa  of  an  inch ;  the 
same  rule  applying  to  all  other  denomination  of  springs. 
After  use,  the  spring  ought  never  be  allowed  to  remain  in  the 
instrument,  but  should  at  once  be  removed,  and  wiped  perfect- 
ly dry ;  otherwise  it  is  liable  in  a  very  short  time  to  become 
corroded  and  pitted  to  such  an  extent,  as  to  render  it  quite  in- 
accurate ;  at  the  same  time  the  inside  of  the  indicator  cylinder 
and  piston,  should  also  before  laying  away  be  made  perfectly 
clean,  and  free  from  all  moisture  arising  from  condensed 
steam. 

Clean  by  means  of  cotton  waste,  or  cloth,  used  in  connec- 
tion with  a  wooden  stick. 


r 

40« 

E'l'l'l1, 

40  . 
>  THE  INCH 

C'N'ITI 

1  11 

120 

I  'I'  I 

'I     *: 
160 

FIG.  43. 

Indicator  Scales.  For  convenience  and  greatly  facilitating 
the  measuring  of  the  diagrams,  special  boxwood  scales,  as 
shown  in  Fig.  43,  are  provided,  upon  which  the  inches  are 


74  Steam  Engine  Indicator 

divided  into  units ;  each  unit  representing  pounds  pressure 
per  square  inch,  corresponding  to  the  number  of  the  spring  in 
use. 

The  edge  upon  which  the  graduations  are  performed, 
is  beviled,  in  order  that  the  marking  may  be  near  the  paper, 
and  consequently  be  more  readily  observed ;  hence  their  use 
will  be  found  much  more  convenient,  than  the  steel  scales 
sometimes  in  use. 

The  Drum  Spring.  The  tension  on  the  drum  spring  illustrat- 
ed in  Fig.  44,  is  a  matter  that  depends  upon  the  good  judg- 
ment of  the  engineer,  and  should  be  just  suffi- 
cient to  keep  the  cord  taut  on  the  backward 
or  inner  stroke  of  the  engine.      The  best  re- 
sults are  obtained  where  the  highest  tension 
FIG.  44.  is  employed,  consistent  with  good  work.     As 

the  speed  of  the  engine  is  increased,  it  is  sometimes  necessary 
to  increase  the  tension  on  the  drum  spring  to  counteract 
the  effect  due  to  the  inertia  of  the  drum  at  the  higher  speed, 
and  provisions  are  usually  made  on  most  indicators,  and  in- 
structions given  whereby  the  tension  on  the  spring  may  be 
varied  to  suit  the  higher  speeds  wherever  necessary. 


And  Its  Appliances.  75 


CHAPTER  X. 


TO    TAKE    DIAGRAMS. 


The  desired  pressure  spring-  being  placed  in  the  instru- 
ment, and  the  paper  in  place  upon  the  drum,  connect  the  cord 
from  the  indicator  to  whatever  form  of  reducing  motion  there 
may  be  at  hand,  (thereby  starting  the  drum  in  motion),  then 
open  the  cock  on  the  pipe  communicating  between  the  steam 
engine  cylinder  and  the  indicator  piston,  (which  in  turn  starts 
the  pencil  movement)  until  a  few  revolutions  of  the  engine 
have  been  made,  or  until  the  instrument  is  heated  to  a  temper- 
ature due  to  the  steam  pressure  present.  During  this  motion, 
examine  the  pencil  mechanism  to  see  that  it  is  moving  freely, 
which  may  be  ascertained  by  placing  the  ringer  directly  against 
and  over  the  top  of  the  piston  rod,  and  by  following  its  motion 
up  and  down ;  the  presence  of  any  grit  between  the  indicator 
cylinder  and  its  piston,  can  readily  be  detected.  If  such 
should  be  found  to  be  the  case  it  will  be  necessary  to  stop  the 
motion  of  the  indicator,  and  remove  the  pencil  mechanism 
with  the  piston  and  thoroughly  clean  and  oil,  before  again 
replacing  in  the  indicator.  Again  set  the  Indicator  in  motion, 
and  after  a  few  revolutions  of  the  engine  have  been  made, 
swing  the  pencil  until  it  comes  in  contact  with  the  paper  on 
the  drum  and  hold  it  there  during  one  complete  revolution  of 
the  engine.  Withdraw  the  pencil  and  close  the  indicator 
cock,  and  immediately  return  the  pencil  to  the  paper 
in  order  to  trace  the  atmospheric  line.  This  should  always 
be  done  as  soon  as  possible  after  tracing  the  card,  so  that 


76  Steam  Engine  Indicator 

it  may  be  drawn  under  about  the  same  conditions  (as  to 
temperature,  etc.)  as  when  the  card  was  taken.  When 
power  is  to  be  measured,  it  is  a  good  plan  to  kee*p  the 
pencil  in  contact  with  the  paper  during  a  number  of  revol- 
utions of  the  engine ;  and  in  measuring  the  diagram,  to  take  a 
line  most  nearly  representing  the  average.  Diagrams  should 
always  be  taken  from  both  ends  of  the  cylinder  where  correct 
conclusions  are  expected. 

Although  "a  diagram  from  one  end  of  the  cylinder  may 
prove  satisfactory,  it  is  not  safe  to  infer  that  one  from  the 
opposite  end  will  be  equally  so ;  but  on  the  contrary  there  will 
often  be  found  a  great  difference  between  diagrams  taken  from 
each  end  of  the  cylinder,  owing  to  the  varying  conditions  of 
pressure,  etc.,  usually  found  in  practice.  Very  often  this 
difference  results  from  improper  or  uneven  valve  setting; 
wherein  the  period  of  opening  or  closing  the  valve,  and  also 
the  point  of  cut-off  differ  at  each  end  in  relation  to  the  stroke 
of  the  engine ;  and  may  'be  partly  due  to  rough  and  tortuous 
steam  passages. 

Sometimes  the  load  may  suddenly  change  during  the  in- 
terval between  the  taking  of  the  first  and  second  diagram, 
causing  a  disparity  between  them  that  might  prove  misleading, 
in  that,  it  would  give  the  appearance  similar  to  that  of  an  un- 
even valve  adjustment,  consequently  after  a  careful  consider- 
ation from  a  number  of  diagrams,  it  becomes  a  requisite  of  the 
engineer  to  use  his  best  judgment  in  deciding  the  cause 
and  applying  the  remedy  for  any  irregular  or  unusal  appear- 
ance of  the  diagram.  This  information  can  only  be  derived 
from  a  careful  application  of  the  indicator  and  a  study  of  the 
diagrams. 

Where  two  indicators  are  used  and  placed  at  each  end  of 
the  cylinder,  the  diagrams  (if  desired)  may  readily  be  taken 
simultaneously;  but  in  case  of  only  one  indicator  at  hand,  it 
must  be  changed  from  one  end  of  the  cylinder  to  the  other ; 


And  Its  Appliances.  77 

in  order  to  obtain  diagrams  from  both,  a  matter  requiring 
considerable  time  and  trouble ;  therefore  it  will  be  found  most 
convenient  in  such  case  to  place  the  indicator  in  connection 
with  a  three-way  cock  (previously  described),  at  the  middle  of 
the  cylinder,  thereby  admitting  steam  from  each  end,  so  that 
diagrams  can  be  taken  from  either  end  of  the  cylinder,  by 
simply  turning  the  handle  of  the  three-way  cock  to  the  required 
position.  This  arrangement  greatly  facilitates  the  labor,  and 
it  also  enables  the  operator  to  produce  diagrams  from  each  end 
of  the  cylinder,  upon  the  same  sheet  of  paper,  and  in  the  short- 
est possible  time;  it  being  very  essential  that  the  second 
diagram  be  taken  as  quickly  as  possible  after  the  first,  in  order 
that  the  conditions  of  speed,  load,  and  pressure  may  remain 
more  nearly  alike  during  the  time  occupied  for  both  tracings. 

It  is  also  more  satisfactory  to  the  engineer  to  take  diagrams 
from  both  ends  of  the  cylinder,  upon  the  same  paper  as  it  en- 
ables him  at  once  to  make  a  discernable  comparison  of  the  pres- 
sures exerted  on  the  opposite  sides  of  the  piston,  throughout 
one  revolution  of  the  engine.  After  all  required  adjustments,  that 
become  necessary  have  been  made,  and  a  satisfactory  diagram 
obtained,  stop  the  motion  of  the  drum  and  remove  the  paper 
therefrom.  Make  memorandum  on  the  paper  of  as  many  of 
the  facts,  as  may  be  required,  such  as  the  style  of  engine, 
where  located,  the  diameter  of  cylinder,  length  of  stroke, 
diameter  of  piston  rod,  the  number  of  revolutions  per  minute, 
which  end  of  cylinder,  the  scale  of  the  spring,  the  vacuum 
in  the  condenser,  the  boiler  pressure,  the  day  and  hour  of  tak- 
ing the  diagram,  and  any  other  factors  that  may  enter  into, 
and  become  necessary  for  an  accurate  consideration  and  solu- 
tion of  the  diagrams. 

For  convenience  of  writing  in  the  data,  and  also  for  filing 
away  for  future  reference,  the  paper  used  upon  the  drum  is  us- 
ually in  the  form  of  printed  blanks  of  suitable  dimensions  to 
fit  the  drum  of  the  indicator,  for  which  they  are  designed,  and 


73 


Steam  Engine  Indicator 


contain  the  heading  of  the  different  principal  factors  necessary 
for  computing  from  the  diagram,  the  horse  power,  water  con- 
sumption, etc.,  of  the  engine.  For  very  expert  tests,  these 


Diagram  trom _ Engine  at _. 

Diameter  of  Cylinder :,-  Diameter,  of  Rod ;  Stroke ;   Clearance _ 

Date. - '18- .    .;  Time ;  Ead  of  Cylinder .......;  Seal*  of  Spring 

Boiler  Gauge ;  Vacuum  Gauge _;  Reaper  minute 

Style. Indicator— •. ;  M.E^R — ._ 'r  l.tLP.. 


FIG.  45. 

blanks  may  be  printed  in  various  forms,  to  suit  any  required 
data  necessary ;  but  the  above  as  shown  in  Fig.  45  will  be  found 
sufficiently  elaborate  for  any  ordinary  indicator  practice. 


And  Its  Appliances.  79 


CHAPTER  XL 


INDICATOR   DIAGRAMS. 


The  important  and  essential  knowledge  to  be  derived  from 
a  careful  investigation  and  study  of  indicator  diagrams  is  in- 
valuable to  the  engineer,  as  they  enable  him  to  easily  ascertain 
and  establish  various  facts  concerning  the  use  of  steam,  that  by 
any  other  method  would  prove  complicated  and  unsatisfactory ; 
of  which  the  following  may  be  stated. 

First.  It  shows  whether  the  valves  of  an  engine  are  cor- 
rectly and  evenly  timed ;  and  also  serves  as  a  guide  in  all 
necessary  adjustments  of  the  same  that  may  be  required,  in 
order  to  insure  the  best  distribution  of  the  steam  working  with- 
in the  cylinder ;  and  thereby  securing  the  maximum  economy, 
and  efficiency  of  the  engine. 

Second.  The  indicator  power  developed  in  the  cylinder  of 
an  engine,  may  be  determined ;  also  the  quantity  of  power  lost 
in  various  ways ;  such  as  leakage  of  valves,  back  pressure,  too 
early  release,  and  incorrect  adjustment  of  valves. 

Third.  It  indicates  whether  the  steam  ports,  and  passages 
are  adequate  in  size,  and  a  diagram  taken  from  the  steam  chest, 
will  also  show  whether  the  steam  pipe  and  its  connections  are 
of  sufficient  size. 

Fourth.  It  indicates  the  condition  of  the  valves  and  pis- 
ton in  reference  to  leakage. 

Fifth.  In  connection  with  a  feed  water  test,  (showing  the 
actual  amount  of  steam  consumed)  the  economy  with  which  the 
engine  works  may  be  determined. 


8o  Steam  Engine  Indicator 

To  ascertain  with,  accuracy,  each  and  every  item  of  infor- 
mation here  mentioned,  it  is  absolutely  essential  that  the  dia- 
gram should  truly  represent  the  motion  of  the  piston;  and  also 
the  pressure  exerted  on  both  sides  of  it,  at  every  point  of  its 
stroke. 

The  general  features  of  a  diagram,  that  indicates  a  proper 

distribution  of  the  steam  in  an  engine  cylinder,  is  represented 

in    Fig.    46,    the   attainment   of  which,  (as   near  as  possible) 

should  be  the  endeavor  of  an  engineer  in  setting  the  valves  of 

3 


FIG.  46. 

his  engine.  A.  A.  is  the  atmosphere  line,  and  B.  B.  represent- 
ing boiler  pressure. 

In  this  diagram  the  initial  steam  pressure,  which  is  the 
highest  pressure  realized  in  the  cylinder,  is  fully  maintained  up 
to  the  commencement  of  cut-off ;  indicating  ample  size  of  steam 
pipes,  ports,  and  other  passages  in  the  engine. 

The  expansion  curve  is  good,  and  the  release  of  the  steam 
is  sufficiently  early  to  secure  a  vfree  exhaust,  also  low,  and  uni- 
form back  pressure. 

The  exhaust  valve  closes  on  the  return  stroke,  in  time  to 
provide  the  necessary  compression,  (or  cushion),  and  thereby 


A  nd  Its  Appliances.  8 1 

counteracting1  in  part  the  effects  of  enertia  and  momentum  of 
the  piston,  cross  head,  and  other  reciprocating  parts,  at  the  end 
of  the  stroke. 

The  admission  of  steam  takes  place  promptly ;  and  projects 
the  admission  line  to  initial  pressure  at  right  angles  (or  per- 
pendicular) to  the  atmospheric  line. 

These  qualities  in  a  diagram  being  an  especial  requisite 
under  any  circumstances,  to  insure  an  economical  working 
engine. 

In  practice  however,  there  will  be  a  great  difference  in  the 
outline  and  appearance  of  the  cards  from  different  engines, 
and  even  from  the  same  engine;  arising  from  numerous  cir- 
cumstances and  conditions  connected  with  it. 

The  diagram  as  before  stated  simply  shows  the  pressure  of 
steam  existing  in  the  cylinder  at  each  part  of  the  revolution  of 
the  engine,  and  it  is  the  province  of  the  engineer  to  determine 
whether  these  pressures  at  each  and  every  point  are  the  correct 
ones ;  and  if  such  is  not  the  case  to  ascertain  wherein  the  fault 
lies,  that  causes  the  error;  then  determine  upon,  and  apply  the 
remedy. 

It  must  be  understood,  that  in  a  great  majority  of  cases, 
the  shape  or  outline  of  the  diagram,  depends  principally  upon 
the  manner  in  which  the  steam  is  admitted  to,  and  released 
from  the  engine  cylinder. 

Therefore,  by  careful  investigation  and  measurement  of 
these  outlines,  and  turning  the  varied  information  which  they 
furnish  to  practical  advantage,  the  real  value  of  the  indicator  is 
readily  made  apparent. 

As  a  preliminary  to  the  study  of  the  diagrams,  suppose  we 
knew  that  at  a  certain  part  of  the  stroke  the  full  boiler  pressure 
should  be  realized ;  now  if  this  does  not  appear  to  be  the  case 
on  the  diagram  there  is  evidently  imperfections  existing,  either 
from  an  incorrect  adjustment  of  the  valves,  or  may  be  due  to 
inadequate  capacity  of  the  steam  pipes,  and  passages  between 


82  Steam  Engine  Indicator 

the  boiler  and  engine  cylinder ;  and  almost  invariably  happens 
also  with  engines  having  insufficient,  or  extremely  light  loads. 

Adversely,  the  diagram  may  show  too  great  a  pressure,  at 
other  certain  points,  when  we  know  that  there  should  be  less  in 
order  that  the  demands  for  good  economy  and  efficiency  in  the 
engine  be  obtained. 

This  latter  circumstance  may  also  proceed  partly  from  in- 
correct valve  adjustment;  although.it  is  principally  caused  by 
leakage  through  the  admission  valves  after  cut-off ;  in  combina- 
tion with  the  re-evaporation  of  steam  previously  condensed 
within  the  cylinder  in  the  early  part  of  the  stroke. 

Any  derangement  of  valve  mechanism  of  the  engine,  such 
as  incorrect  position  of  the  eccentric,  on  the  shaft  or  an  uneven 
adjustment  in  the  length  of  the  valve  rods  and  connections, 
will  in  consequence,  be  revealed  in  the  diagram,  by  late  admis- 
sion or  release,  by  low  initial,  or  high  back  pressure,  also  by 
absence  of  compression  ;  either  of  which  in  performing  an  equal 
amount  of  work  will  result  in  an  increased  consumption  of 
steam. 

Consequently  where  discrepancies  of  any  kind  occur,  a 
thorough  investigation,  study,  and  reasoning  of  the  diagram 
first  becomes  necessary,  in  order  to  intelligently  locate  the 
cause  of  the  defect,  and  make  changes,  and  corrections  accord- 
ingly until  the  diagram  shows  a  proper  distribution  of  steam 
pressure  throughout  the  stroke  of  the  engine. 


fe 


A  nd  It  s  Applia  nces  8  3 


CHAPTER  XII. 


STUDY   OF   DIAGRAMS. 


To  the  Steam  Engine  Indicator  (it  may  be  said),  belongs 
the  credit  of  furnishing  a  great  part  of  the  information  that 
has  enabled  scientific  engineers,  (and  others  who  have  studied 
the  subject)  to  apply  intelligently  and  successfully,  and  has 
hereby  contributed  in  a  great  measure  to  the  present  perfec- 
tion of  our  modern  steam  engines. 

The  most  correct  and  best  means  of  obtaining  a  knowledge 
of  the  internal  workings  of  the  steam  in  a  cylinder  under  differ- 
ent circumstances  of  loads  and  pressures  is,  by  a  careful  study 
of  what  are  designated  as  Indicator  Diagrams. 

A  diagram  from  one  end  of  a  steam  engine  cylinder  shows 
the  exact  pressure  acting  upon  the  engine  piston,  at  any  and 
every  part  of  its  movement,  during  the  time  of  one  complete 
revolution  on  both  forward  and  return  stroke  of  the  engine ; 
and  to  show  a  corresponding  pressure  on  the  other  side  of  the 
piston,  another  diagram  must  be  taken  from  the  opposite  end 
of  the  cylinder. 

The  outline  of  the  figure  traced  by  the  pencil  upon  the  paper 
of  .the  indicator  drum,  depends  upon  the  variable  pressure  of 
steam  in  the  cylinder,  acting  upon  the  engine  piston,  through- 
out one  complete  revolution  of  the  engine,  in  combination 
with  the  horizontal  length  of  the  figure  produced  by  the  rota- 
tive motion  of  the  paper  drum. 


84  Steam  Engine  Indicator 

If  the  steam  be.  admitted  to  the  cylinder  at  the  commence- 
ment of  the  stroke  and  continued  at  a  uniform  pressure,  and 
exhausted  at  the  extreme  end,  and  from  thence  returning  to 
its  beginning,  it  will  have  traced  a  figure  on  the  paper,  bearing 
a  close  approximation  to  a  parallelogram,  or  rectangle. 

If  the  admission  of  steam  had  been  cut  off,  after  only  a 
part  of  the  stroke  had  been  completed,  (leaving  the  amount  to 
expand  to  the  end  of  the  stroke)  the  diagram  will  assume  a 
shape  somewhat  similar  to  that  represented  in  Fig.  47. 

In  the  matter  of 

a  { 

details  these  two  rep- 
resentative forms  may 
have  innumerable 
modifications. 

We  have  selected 
Fig.  47  as  exhibiting 
the  essential  features 
.and  events  (d tiring 
•  the  stroke  of  the  en- 


lj 

FIG.  47.  gine),  of   a  well   pro- 

portioned diagram,  showing  the  action  and  pressures  of  steam 
that  usually  take  place  in  the  engine  cylinder.  This  diagram 
shows  that  the  admission  of  steam  commences  at  A  and  con- 
tinues to  the  point  C,  where  cut-off  commences,  and  is  com- 
plete at  D ;  the  expansion  is  from  D  to  E ;  the  exhaust  begins 
to  open  at  E  and  closes  at  G ;  the  back  pressure  is  represented 
by  the  line  from  F  to  G,  and  continuing  to  A.  The  compres- 
sion of  the  steam  remaining  after  the  exhaust  closes,  begins  at 
the  point  G,  and  ends  at  the  admission  line  A,  B ;  this  com- 
pression producing  a  continual  increasing  back  pressure  to  the 
point  A. 

The  point  T  is  where  the  expansion  line  would  have 
reached  provided  the  exhaust  had  remained  closed  to  the  end 
of  the  stroke,  and  is  designated  the  Terminal  Pressure. 


And  Its  Appliances.  85 

The  line  H,  I,  represents  the  atmospheric  line ;  and  the 
different  events  of  the  stroke,  appearing  on  the  diagram  at 
various  heights  above  the  atmospheric  line  are  measured  from 
that  line,  in  pounds  pressure  by  a  scale  corresponding  with  the 
spring  used,  in  producing  the  diagram ;  and  consequently  the 
location  of  these  points  in  reference  to  each  other,  becomes  an 
index  to  the  engineer,  and  serves  as  a  guidance  to  him,  in  the 
study  of  engine  performance  and  in  the  steam  economy  of 
engines. 

It  is  advisable  in  most  cases  to  take  the  diagrams  from  both 
ends  of  the  cylinder,  on  the  same  sheet  of  paper,  as  shown  in 
Fig.  48,  (by  the  use  of  the  three-way  cock,  as  recommended  in 

a  former  chapter)in  order 
to  facilitate  the  matter 
of  making  a  comparison 
between  the  diagrams 
from  each  end  of  the 
cylinder,  more  readily, 
and  thus  showing  the 
varying  pressure  at  dif- 
ferent events  of  the 

stroke,  in  both  ends  of 
FIG.  48.  ,,  ,.    -,  , 

the    cylinder;    such    as 

Reproduction  of  an  actual  card  taken  from  a  9^  in.  x  9  ; 

Westinghouse  engine— 325  revolutions  per  minute.  admission       of      Steam, 

point  of  cut-off,  release,  or  opening  of  exhaust,  closure  of  ex- 
haust, compression,  etc.,  and  thereby  showing  any  errors  or 
discrepancies  in  the  adjustment  of  the  valve,  or  valves,  that 
regulates  and  controls  the  flow  of  steam  to  and  from  each  end 
of  the  steam  cylinder,  and  which  thereby  enables  the  engineer 
to  arrive  at  correct  conclusions  in  reference  to  faulty  valve  mo- 
tions and  methods  of  correcting  them ;  which  by  any  other  way 
is  a  difficult  task  to  accomplish,  with  any  certainty,  that  the  re- 
quirements of  a  correct  valve  motion  are  attained. 


86  Steam  Engine  Indicator 

An  Indicator  Diagram  is  the  result  of  two  movements, 
which  are  at  right  angles  to  each  other ;  one  of  which  is  the 
rotation  of  the  paper  drum,  forward  and  back,  around  its  cen- 
tral stud,  and  is  produced  on  a  reduced  scale,  coincident  with 
and  by  the  movement  of  the  engine  cross-head,  and  thereby 
tracing  a  horizontal  line  on  the  paper  drum,  at  any  time  a  con- 
tact is  made  between  the  drum  and  pencil. 

The  other  is  the  vertical  movement  of  the  pencil,  parallel 
to  the  axis  of  the  drum  and  is  produced  by  the  steam  pressure, 
acting  on  the  piston  of  the  indicator,  and  forcing  it  to  a  height 
proportionate  to  the  pressure  upon  the  piston ;  consequently 
the  length  of  the  diagram  represents  the  stroke  of  the  engine 
on  a  reduced  scale ;  while  the  vertical  height  at  any  given 
point,  represents  the  pressure  upon  the  Indicator  piston,  at  a 
corresponding  point  in  the  stroke  of  the  engine. 

The  height  to  which  the  pencil  will  ascend,  depends  en- 
tirely on  the  pressure  exerted  upon  the  piston,  and  the  denom- 
ination of  the  spring  used,  and  is  measured  in  pounds 
pressure  per  square  inch,  at  any  given  point  in  the  length  of 
the  diagram,  by  a  scale,  or  rule,  divided  in  a  number  of  units 
per  lineal  inch,  to  correspond  with  the  denomination  of  the 
spring. 

The  denomination  or  number  of  any  particular  spring,  is 
one  that  requires  the  same  number  oi  pounds  pressure  per  square 
inch  on  the  indicator  piston,  to  compel  the  pencil  to  move  one 
inch  in  vertical  height,  against  the  resistance  of  said  spring. 

By  placing  a  spring  in  the  indicator  and  connecting  the  cord 
so  as  to  give  motion  to  the  paper  drum,  (and  before  admitting 
steam  to  the  instrument)  a  horizontal  line  may  be  drawn,  by 
bringing  the  pencil  in  contact  with  the  paper  on  the  drum. 

This  line  is  called  the  atmospheric  line,  and  from  which, 
as  a  zero  line,  all  pressures  are  measured  in  a  vertical  direction 
from  the  same,  whether  above  or  below  the  line.  All 


And  Its  Appliances.  87 

measurements  above  the  atmospheric  line  represents  positive 
pressure,  while  below  the  line,  show  negative  pressure. 

For  each  indicator  spring,  there  is  usually  provided  a 
special  scale,  or  rule,  for  the  different  denominations.  For 
example :  A  diagram  that  has  been  taken  where  a  No.  40 
spring  was  used  in  the  indicator,  (designated  a  40  pound 
spring)  should  be  measured  by  a  scale  that  is  divided  in  40 
parts  to  each  lineal  inch ;  each  division  in  vertical  height, 
above  the  atmospheric  line  representing  one  pound  pressure 
per  square  inch  on  the  indicator  piston. 

In  the  various  computations  and  study  of  diagrams,  for 
the  purpose  of  ascertaining  the  Mean  Effective  Pressure  on  the 
Engine  Piston;  Horse  Power;  Steam  Consumption,  &c.,  and 
also  for  plotting  the  hyperbolic  curve,  it  becomes  necessary  to 
establish  what  is  called  the  vacuum  line,  or  line  of  no  pressure, 
which  should  be  located  parallel  with  the  atmospheric  line, 
and  at  a  distance  below  it,  equal  to  14.7  pounds,  by  the  scale 
corresponding  with  the  scale  of  the  spring  with  which  the  dia- 
gram was  taken. 

Another  and  important  factor  pertaining  to  the  same 
study,  is  the  clearance  line,  which  is  drawn  perpendicular  to  the 
atmospheric  line  and  located  at  the  steam  admission  end  of  the 
diagram ;  and  at  such  distance  from  it,  as  will  bear  the  same 
proportion  to  the  length  of  the  diagram,  as  the  volume  of  the 
clearance  space  bears  to  the  piston  displacement ;  or  that  vol- 
ume which  is  equal  to  the  area  of  the  steam  cylinder  multiplied 
by  the  stroke  of  the  piston. 

The  clearance  is  the  amount  of  waste  room  between  the 
steam  valve  and  the  engine  piston  when  at  its  extreme  end  of 
the  stroke,  and  which  has  to  be  filled  with  steam  at  initial 
pressure  at  each  end  of  the  cylinder,  for  every  revolution  of 
the  engine. 

The  required  amount  of  steam  for  this  purpose  comes 
either  directly  from  the  boiler,  or,  by  the  compression  of  the 


88 


Steam  Engine  Indicator 


steam  that  remains  in  the  cylinder  after  an  early  closure  of  the 
exhaust  valve,  or  from  both  combined.  The  amount  of  clear- 
ance varies  in  different  styles  of  engines.  In  slow  running 
engines,  this  variation  usually  amounts  to  from  two  to  five  per 

cent.,  whereas  for  high 
speeds  it  may  reach 
from  two  to  ten  or 
twelve  per  cent.,  or 
even  more. 

The  finding  of  the  ex- 
act amount  of  the  clear- 
ance (in  the  absence  of 
any  data  fiom  the  man- 
ufacturer of  the  en- 
gine), is  often  a  diffi- 
cult matter,  but  may  be 
Fia  49-  roughly  approximated 

in  most  cases,  either  by  computation  from  measurements  of 
the  space  between  the  valve  and  piston,  when  at  its  end  of 
stroke ;  or  it  may  be 
accurately  deter- 
mined, (where  the 
valves  and  piston  are  ^ 
tight)  by  filling  the  *Cj 
space  with  water  from  a  ^ 
receptacle  containing  a  $ 
quantity  that  has  been  ^ 
previously  weighed  or  *t 
measured,  and  its  vol-  ^ 
ume  ascertained.  In 
many  cases  however  * 
this  is  not  practicable, 


&P  '/  e  r/c    ^  '*"  ^ 


FIG.  50. 


and  is  almost  impossible,  with  engines  that  have  been  in  use 
and  neglected  until  the  valves  and  piston  become  leaky,  and 


And  Its  Appliances. 


89 


thereby  preventing  any  chances  of  accuracy  in  the  matter. 
Sometimes  the  only  knowledge  regarding  the  amount  of  clear- 
ance has  to  be  obtained  from  the  diagram  itself. 

If  this  has  well  denned  expansion  and  compression  curves 
the  clearance  line  on  the  diagram  may  be  closely  determined, 
by  a  graphical  method,  from  either  curve ;  as  shown  in  Figs. 
49  and  50  as  follows;  Select  two  points,  (preferably)  on  the 
compression  curve^Fig.  49,  as  far  apart  as  .possible,  but  within 
the  limits  of  the  true  curve,  and  draw  a  line  connecting  the 
two  points,  which  will  represent  one  of  the  diagonals  of  a  rec- 
tangle described  on  the  curve,  of  which  two  sides  are  parallel 
to  the  atmospheric  line. 

If  now  a  diagonal  be  drawn  through  the  opposite  corners 
of  the  rectangle  and  extended  to  the  vacuum  line ;  then  a  per- 
pendicular drawn  from  the  point  of  intersection,  will  be  the 
approximate  clearance  line;  and  the  distance  of  this  line  from 
the  end  of  the  diagram,  divided  by  the  total  length  of  the  dia- 
gram will  give  the  percentage  of  clearance  in  the  engine. 

Another  method 
of  approximately  as- 
certaining the  clear- 
ance is  shown  in  Fig. 
51,  the  results  of 
which  coincide  exact- 
ly with  Fig.  49,  but 
is  given  as  being 
rather  more  simple  in 
its  application. 

Draw  the  straight 
j  line  A.  E.  from  a  point 
^"  "^  on   the   vacuum    line 

Eia  51'  (as  at  A.)  in  a  direc- 

tion as  will  cut  the  compression  curve  at  two  points  B.  and  C. 
and  continue  it  beyond  the  end  of  the  diagram  as  at  E.  Now 


90  ^>ieam  Engine  Indicator 

with  a  pair  of  dividers,  set  one  leg  on  the  point  A.  and  adjust 
the  other  to  point  B.  and  with  this  distance  so  taken,  place 
one  point  of  the  dividers  on  point  C.  and  describe  a  line  inter- 
secting the  line  A.  E.  at  D. 

If  a  perpendicular  be  now  drawn  from  the  vacuum  line 
through  this  intersection,  then  its  distance  from  the  end  of 
the  diagram  will  represent  the  clearance  of  the  engine. 

The  amount  of  clearance  in  an  engine  is  an  important  fac- 
tor, and  is  always  considered  in  the  study  of  steam  economy 
as  a  source  of  loss ;  therefore  in  the  designing  of  the  various 
styles  of  engines,  it  has  always  been  one  of  the  principal  in- 
tentions with  engine  designers,  to  construct  them  with  a  view 
of  reducing  the  clearance  to  a  minimum  and  thereby  saving 
(in  a  measure)  the  amount  of  steam  required  to  fill  large  clear- 
ance spaces. 

A  reduction  of  clearance  has  an  effect  to  produce  a  lower 
terminal  pressure,  for  any  given  cut-off;  and  also  greater 
mean  effective  pressure  for  a  given  terminal ;  both  of  which 
are  conducive  to  good  economy. 

A  loss  takes  place  from  the  clearance,  when  the  steam  is 
exhausted  at  a  higher  pressure  than  the  back  pressure,  or,  that 
pressure  which  exists  on  the  return  stroke  and  consequently  a 
reduction  of  clearance,  also  reduces  this  loss  of  steam 


And  Its  Appliances.  91 


CHAPTER  XIII. 


LINES   AND    POINTS    OF   THE   DIAGRAMS. 


The  diagram  shown  in  Fig.  52,  is  presented  in  this  chap- 
ter, to  more  fully  designate  by  name  the  various  lines,  points, 
and  curves,  that-  in  combination  serves  to  make  it  complete, 
and  also  shows  the  lines  dotted,  that  in  most  cases  become  nec- 
essary to  be  added  by  hand,  in  order  to  assist,  and  facilitate  in 
all  matters  attending  the  accuracy  of  any  calculations  that  may 
arise  in  reference  to  indicator  diagrams. 

The  following  names  are  generally  applied  to  the  various 
lines  and  curves  of  the  diagram . 

H.  I.  is  the  Atmospheric  Line,  and  is  traced  by  the  indicator 
at  a  time  when  communication  between  the  engine  cylinder, 
and  indicator  piston  is  closed,  and  the  atmosphere  having  free 
access  to  both  sides  of  the  piston  of  the  indicator. 

V.  V.  is  the -Vacuum  Line,  drawn  by  hand  in  dotted  lines, 
and  represents  the  line  of  perfect  vacuum  or  absence  of  all 
pressure. 

It  is  drawn  I4TV  pounds,  (by  the  scale  of  the  spring  with 
which  the  diagram  is  taken)  below  the  atmospheric  line ;  that 
being  the  mean  pressure  at  sea  level. 

V.  K.  is  the  Clearance  Line,  shown  drawn  by  hand  in 
dotted  lines,  at  such  a  distance  from  the  end  of  the  diagram, 
as  will  represent  the  total  clearance  or  waste  room  between  the 


92  Steam  Engine  Indicator 

face  of  the  valve,  and  the  piston,  when  the  engine  is  at  either 
extreme  end  of  the  stroke. 


FIG.  52. 

Its  distance  from  the  diagram  is  usually  reckoned  in  per 
cent,  of  the  piston  displacement,  and  in  Fig.  52,  shows  about 
4  per  cent,  of  clearance. 

A.  B.  is  the  Admission  Line,  and  its  height  above  the  at- 
mospheric line  represents  the  pressure  due  to  the  admission  of 
steam  to  the  engine  cylinder. 

It  is  usually  very  nearly  perpendicular  to  the  atmospheric 
line,  for  the  reason  that  the  admission  of  steam  takes  place 
very  quickly,  and  at  a  time  when  the  piston  of  the  engine  is 
moving  very  slowly,  or  nearly  stationary. 

B.  is  the  point  of  Initial  Pressure  and  is  the  first  pressure 
realized  at  the  beginning  of  the  stroke  of  the  engine. 

B.  C.  D.  is  the  Steam  Line,  and  is  traced  during  the  time 
the  steam  is  being  admitted  to  the  cylinder,  or  until  cut-off 
takes  place. 


And  Its  Appliances.  93 

D.  is  the  Absolute  Point  of  cut-off  and  is  the  point  where 
the  valve  closes  and  thereby  prevents  any  further  admission  of 
steam  to  the  engine  cylinder. 

Owing  to  their  peculiar  formations,  many  diagrams  do  not 
show  clearly,  (from  observation  alone)  the  exact  point. 

D.  E.  is  the  Expansion  Curve,  and  represents  the  gradual 
fall  of  pressure  due  to  the  expansion  of  the  steam  remaining 
in  the  cylinder  after  cut-off  takes  place,  and  continuing  to  the 
end  of  the  stroke. 

E.  is  the  Point  of  Exhaust,  and  is  located  where  the  exhaust 
valve  begins  to  open ;   thereby  releasing  or  exhausting   the 
steam  from  the  cylinder ;  and  like  the  point  of  cut-off,  is  some- 
times difficult  of  exact  location. 

E.  F.  is  the  Exhaust  Line,  which  descends  suddenly  and  is 
traced  during  the  interval  that  occurs,  between  the  time  the 
exhaust  valve  begins  to  open,  and  the  end  of  the  stroke. 


FIG.  53. 

In  diagrams  like  Fig.  53,  where  the  pressure  has  gradu- 
ally fallen  during  expansion,  sufficiently  low,  to  coincide  with 
the  return  or  back  pressure,  this  line  does  not  appear. 

And  in  diagrams  like  Fig.  54,  where  the  expansion  curve 
falls  below  the  back  pressure,  before  the  end  of  the  stroke, 


94 


Steam  Engine  Indicator 


(causing  a  partial  vacuum  in  the  cylinder  thereby),  the  exhaust 
line  is  ascending  until  it  agrees  with,  and  merges  into  the  back 
pressure  line. 


FIG.  54. 

This  action  indicates  a  rapid  flow  of  the  steam  from  the 
exhaust  pipe,  back  into  the  cylinder;  thereby  restoring  the 
pressure  lost  through  the  expansion  curve  falling  below  the 
back  pressure  line,  during  the  latter  half  of  the  stroke. 

F.  G.  is  the  Back  Pressure  Line,  and  represents  the  pres- 
sure opposing  the  piston  on  its  return  movement,  and  for  this 
reason  is. called  Back  Pressure. 

In  diagrams  from  non-condensing  engines  it  either  coincides 
with,  or  is  above  the  atmospheric  line ;  while  in  condensing  en- 
gine it  is  below  the  atmospheric  line,  at  such  a  distance  as  cor- 
responds with  the  vacuum  obtained  in  the  engine  cylinder ; 
and  in  either  case  it  acts  as  back  pressure. 

G.  is  the  point  of  Exhaust  Closure,  and  is  where  the  ex- 
haust valve  closes ;  thereby  preventing  the  further  escape  of 
the  steam  from  the  cylinder. 


And  Its  Appliances.  95 

Like  the  point  of  cut-off  and  exhaust,  it  cannot  in  all  cases 
be  located  very  exactly  from  observation ;  on  account  of  the 
change  of  pressure,  due  to  a  more  or  less  gradual  closing  of 
the  valve,  which  will  cause  its  exact  location  to  be  rather 
undefined. 

G.  A.  is  the  Compression  curve,  and  is  a  result  of  the  rise 
in  pressure  due  to  the  compression  (from  the  return  motion  of 
the  piston),  of  the  steam  remaining  in  the  cylinder,  after  the 
exhaust  valve  closes. 

In  cases  where  the  exhaust  remains  open  until  the  end  of 
the  stroke,  this  line  does  not  appear  on  the  diagram. 

T.  is  the  point  of  Terminal  Pressure,  and  is  an  indispensa- 
ble factor  in  many  calculations  pertaining  to  diagrams. 

It  may  be  located  by  a  continuation  of  the  expansion  curve 
from  E,  to  the  end  of  the  diagram  at  T,  as  shown  in  Fig.  52, 
and  its  height  above  the  line  of  perfect  vacuum,  V.  V.  repre- 
sents the  absolute  pressure  that  would  exist  at  the  end  of  the 
stroke ;  providing  the  release  of  the  steam  in  the  cylinder  does 
not  take  place  earlier. 

This  pressure  is  always  measured  from  vacuum  line  V.  V. 
hence  it  is  the  absolute  Terminal  Pressure. 

Initial  Expansion,  is  the  fall  in  pressure  that  takes  place 
through  expansion  during  the  interval  between  the  admission 
of  steam,  and  absolute  point  of  cut-off. 

It  is  represented  in  the  diagram,  Fig.  52,  by  the  dotted 
line  B.  P.  and  is  generally  considered  an  undesirable  feature, 
especially  in  automatic  cut-off  engines. 

T.  i.  and  T.  2,  in  dotted  lines,  are  made  use  of  in  calcula- 
tions connected  with  the  water  or  steam  consumption  of  the 
engine,  per  indicated  horse  power,  as  shown  by  the  diagram ; 
and  which  will  be  referred  to  hereafter. 

The  Mean  Effective  Pressure,  as  before  noted,  is  the  differ- 
ence between  the  average  of  all  the  varying  pressures  acting 
against  the  engine  piston,  in  impelling  it  forward ;  and  that  of 


96  Steam  Engine  Indicator 

all  the  average  pressure  which  tends  to  retard  its  motion ;  and 
is  another  indispensable  factor  in  the  computations  of  the  dia- 
gram; and  is  expressed  thus:  M.  E.  P. 

The  point  of  cut-off  is  an  important  event  in  the  stroke  of 
the  engine,  and  is  located  at  a  place  on  the  diagram,  where  the 
steam  valve  absolutely  closes;  as  at  D,  Fig.  52,  and  thereby 
prevents  the  further  admission  of  steam  to  the  cylinder  during 
the  stroke. 

With  slow  speed  engines,  and  quick  releasing  gear,  the 
point  of  cut-off  will  be  fairly  well  defined ;  but  with  the  higher 
speeds,  relative  to  the  time,  or  period  required  from  the  com- 
mencement, to  the  absolute  closure  of  the  valve,  it  will  enable 
the  piston  to  travel  a  certain  distance  during  that  time,  (more 
or  less  according  to  circumstances)  and  which  will  cause  the 
steam  line  to  be  rounded  off,  to  meet  the  expansion  line,  and 
consequently  the  point  at  which  the  valve  actually  closes,  can 
only  be  approximately  determined  by  noting  the  point  at  which 
the  curve  from  the  steam  line  changes  and  begins  to  concave 
inward;  thence  continuing  on,  to  exhaust  opening,  thereby 
forming  and  completing  the  expansion  curve. 

In  many  cases  it  is  almost  impossible  to  determine  the 
point  of  cut-off  even  in  this  manner,  owing  to  the  various  dis- 
torted formations  of  the  lines  of  the  diagram  near  this  point. 


And  Its  Appliances.  97 


CHAPTER   XIV. 


ISOTHERMAL    CURVE. 


A  careful  comparison  and  examination  of  the  hyperbolic 
curve,  with  the  expansion  curve  of  a  properly  jacketed  steam 
cylinder,  with  tight  piston  and  valves,  has  demonstrated  that 
the  two  curves  conform  with  each  other  very  nearly,  in  all  re- 
spects ;  therefore  assuming  that  the  expansion  line  should  be 
a  hyperbolic  curve,  then  the  principle,  upon  which  this  curve 
is  constructed,  furnishes  an  easy  and  ready  method  of  locating 
the  theoretical  point  of  cut-off,  for  any  particular  point  select- 
ed on  the  expansion  line  of  the  actual  diagram.  The  hyper- 
bola, sometimes  called  the  Isothermal  curve,  is  constructed  on 
the  principle  established  by  Mariotte,  in  reference  to  the  com- 
pression of  gases,  and  known  as  the  Mariotte  law ;  and  is  gen- 
erally expressed  as  follows : 

''The  temperature  remaining  the  same,  the  volume  of  a 
given  mass  of  gas,  is  in  inverse  ratio  to  the  pressure  which  it 
sustains.  And  this  may  be  held  to  be  substantially  correct 
within  a  considerable  range  of  pressure ;  therefore  according 
to  this  law,  if  steam  of  100  pounds  absolute  initial  pressure, 
per  square  inch,  be  admitted  to  a  steam  engine  cylinder  (ignor- 
ing clearance  in  the  matter),  during  one-half  of  the  stroke,  and 
admission  stopped  at  that  point ;  and  allowing  the  volume  at  that 
pressure  to  expand  during  the  balance  of  the  stroke,  the  vol- 
ume will  be  doubled,  with  a  reduction  of  pressure,  of  one-half, 


98  Steam  Engine  Indicator 

or  50  pounds  per  square  inch  at  the  end  of  the  stroke.  If,  in 
this  example,  the  admission  of  steam  had  been  stopped  at  one- 
quarter  of  the  length  of  the  stroke,  the  volume  of  that  amount 
of  steam  at  half -stroke  would  have  been  doubled,  but  with  a  re- 
duced pressure  of  one-half,  (or  50  pounds  per  square  inch). 
At  three-fourth  stroke,  the  volume  would  be  three  times,  at 
one-third  pressure  (or  33^  pounds),  and  at  the  end  of  the 
stroke,  the  volume  would  be  increased  four  times,  and  result 
in  a  pressure  of  one-fourth  initial  (or  25  pounds  per  square 
inch),  hence,  the  distance  from  the  clearance  line  of  a  diagram, 
to  any  point  on  the  expansion  line,  if  multiplied  by  the  pres- 
sure at  such  point,  the  product  will  be  the  same  wherever  loca- 
ted, and  this  fact  furnishes  a  simple  rule  for  determining  any 
number  of  points  through  which  the  curve  must  pass,  by  tak- 
ing the  product  of  any  point,  (by  such  multiplication),  as  a 
constant  number,  and  dividing  it  by  other  distances  from  the 
clearance  for  corresponding  pressures,  or  by  other  pressures 
for  distance  from  the  clearance  line.  The  properties  of  the 
hyperbola  therefore  enables  us  to  locate  points  on  the  curve  by 
an  arithmetical  method,  described  and  represented  in  Fig.  55. 


First  draw  the  absolute  vacuum,  or  zero  line  V,  at  a  distance 
equal  to  14.7  pounds  by  the  scale  of  the  spring  below,  and 
parallel,  with  the  atmospheric  line  H.  I.  Then  locate  the 
clearance  line  K,  in  accordance  with  the  best  data  at  hand,  in 


And  Its  Appliances.  99 

reference  to  what  its  distance  should  be  from  the  end  of  the 
diagram. 

Draw  A,  E,  to  represent  the  boiler  pressure.  Select  the 
point  of  cut-off  on  the  diagram  (as  near  as  possible  from  obser- 
vation, as  at  X),  and  draw  a  line  through  it,  perpendicular  to 
the  vacuum  line,  and  intersecting  it  at  point  3,  and  the  line  A, 
E,  at  C,  and  this  line  is  called  the  cut-off  line.  The  point  C, 
will  then  be  the  commencement  of  the  hyperbolic,  or  theoreti- 
cal curve.  The  vertical  height  of  the  line  3,  C,  (above  the 
zero  line),  represents  the  pressure  of  steam,  at  the  point  of  cut- 
off C ;  the  diagram  showing  that  pressure  to  be  100  pounds  per 
square  inch,  (measured  by  the  scale  of  the  spring  No.  80). 
The  distance  from  the  clearance  line  K,  to  cut-off  line  3,  C, 
will  represent  its  volume. 

Divide  this  volume,  or  distance,  into  any  convenient  num- 
ber of  equal  parts,  (it  is  shown  divided  into  three  parts  in  Fig. 
55),  then  take  the  length  of  one  such  division,  and  (with  a  pair 
of  dividers,  or  otherwise),  commencing  at  the  clearance  line  K, 
space  on  the  vacuum  line  whatever  number  of  these  equal  di- 
visions, that  may  be  contained  in  the  length  of  the  diagram, 
and  erect  perpendicular  lines  (a  little  above  the  actual  curve), 
from  each  division.  These  lines  are  designated  as  ordinates, 
and  numbered  consecutively  i,  2,  3,  4,  &c.,  beginning  with 
the  one  nearest  to  the  clearance  line.  It  is  immaterial  whether 
the  spacing  comes  out  even  with  the  end  of  the  diagram ;  but 
in  cases  where  they  do  not,  it  is  only  necessary  to  make  an  ad- 
ditional spacing  that  will  extend  beyond  the  length  of  the  dia- 
gram, (as  shown  in.  Fig.  55),  and  treat  it  the  same  as  the  other 
points.  Now  in  order  to  utilize  the  properties  of  the  hyperbola 
in  laying  out  the  theoretical  curve,  it  will  be  necessary  to  draw 
short  lines  cutting  the  ordinates  at  the  proper  height,  meas- 
ured vertically  from  the  vacuum  line ;  so  that  if  the  pressure  at 
anyordinate,  be  multiplied  by  the  number  representing  the  volume 
of  the  same  ordinate,  the  product  will  always  be  the  same,  at 


IOO  Steam  Engine  Indicator 

whatever  point  selected ;  for  example  :  Suppose  on  being  meas- 
ured by  the  scale  of  the  diagram,  (No.  80)  the  height  of  the 
point  of  cut-off  C,  from  the  vacuum  line  V,  be  found  to  show 
an  absolute  pressure  of  100  pounds  per  square  inch  ;  with  a  vol- 
ume equal  to  three  of  the  divisions,  into  which  the  diagram  has 
been  divided.  Then  100  pounds  multiplied  by  3,  equals  300; 
which  will  be  our  constant  number,  to  be  divided  for  all  other 
pressures  or  volumes.  Consequently  the  height  at  which  the  hy- 
perbola will  cut  any  desired  ordinate,  may  be  found  by  dividing 
the  constant  300,  by  the  number  of  the  ordinate;  that  is  the 
height  of  ordinate  4,  is  found  by  dividing  300-=- 4=  75,  and  in 
the  same  manner  the  height  of  ordinate  5  is  found  by  300-^  5  = 
60,  or  300-^-6^50,  &c.,  which  will  be  the  heights  to  be  set  off 
in  divisions  of  the  scale  (each  division  representing  pounds 
pressure),  at  the  different  ordinates.  If  so  desired,  the  con 
struction  of  the  curve  may  be  commenced  either  at  the  termi- 
nal pressure,  or  just  before  the  point  of  release,  and  points  lo- 
cated on  the  ordinates,  in  the  opposite  direction  by  the  same 
method.  In  this  case  the  terminal  shows  an  absolute  pressure 
of  25  pounds,  per  square  inch;  and  having  a  volume  of  12  di- 
visions; therefore  25  X  12  —  300,  which  if  divided  by  the  num- 
ber representing  any  other  volume  or  ordinate,  we  have  the 
same  results  for  pressure  as  by  the  first  method.  Instead  of 
using  the  height  of  the  lines  to  represent  pressure,  they  may 
just  as  well  be  considered  to  represent  inches,  and  fractions  of 
an  inch,  as  follows :  the  vertical  height  of  the  point  of  cut-off 
C,  from  the  zero  line  V,  being  i^  inches,  and  on  ordinate  3, 
therefore  3X  i/^  =  3-75  inches,  which  is  our  constant  number 
by  this  method.  Hence  3. 7-5 -=-5  =  . 75  of  an  inch,  which  will 
be  the  height  of  the  point  above  the  vacuum  line,  on  ordinate 
5,  through  which  the  curve  will  pass,  and  the  heights  of  all 
other  points  may  be  found,  by  dividing  the  constant  3.75  inches, 
by  the  number  representing  each  ordinate.  The  heights  of  all 
points  must  be  measured, from  the  vacuum  line. 


A  nd  Its  Appliances. 


101 


The  location  of  the  vacuum  line  may  also  be  ascertained 
by  dividing  the  'pressure  of  the  atmosphere,  14.7  pounds,  by 
the  scale  of  the  spring,  and  the  quotient  will  be  in  inches ;  for 
example:  14.7-^-80— .  183  of  an  inch  below  the  atmospher- 
ic line.  This  method  of  constructing  the  hyperbola,  or  isother- 
mal curve,  as  represented  in  Fig.  55,  is  intended  to  show  more 
particularly,  the  principle  upon  which  the  curve  is  projected, 
rather  than  to  lay  any  claim  to  simplicity.  There  are  various 
geometrical  methods,  much  more  preferable,  for  projecting  the 
theoretical  curve ;  all  of  which  give  about  the  same  results,  as 
the  one  described. 

One  simple  and  convenient  plan  of  doing  it,  is  represented 


FIG.  56. 

in  Fig.  56,  and  is  as  follows:  Draw  the  vacuum  line  V,  Vi, 
parallel  with  the  atmospheric  line  H,  I ;  at  a  distance  below  it 
representing  14.7  pounds,  by  the  scale  of  the  diagram;  also 
draw  A,  E,  parallel  to  the  atmospheric  line  to  represent  the 
boiler  pressure,  erect  the  clearance  line  K,  at  a  distance  from 
the  end  of  the  diagram,  that  will  represent  the  percentage  of 
clearance  in  the  engine ;  said  line  being  perpendicular  to  and 
cutting  the  vacuum  line  at  V.  Select  any  point  on  the  actual 
curve,  before  commencement  of  the  exhaust;  as  at  B,  and  from 
that  point  draw  a  vertical  line,  cutting  A,  E,  at  E,  From  E, 


IO2  Steam  Engine  Indicator 

draw  the  diagonal  E,  V,  and  from  B,  draw  a  line  parallel  with, 
the  atmospheric  line,  intersecting  the  diagonal  E,  V,  at  D. 
From  this  intersection  at  D,  erect  a  perpendicular  cutting  A, 
E,  at  the  point  C.  Then  C  will  be  the  theoretical  point  of  cut- 
off, and  D,  C,  is  called  the  cut  off  line.  From  C,  mark  off  any 
desired  number  of  points  on  A,  E,  as  i,  2,  3,  4,  &c.,  and  draw 
a  perpendicular  from  each  toward  the  atmospheric  line;  also, 
from  the  same  points,  draw  diagonals  to  the  vacuum  point  V. 
At  the  intersection  of  the  diagonals  with  the  cut-off  line  D,  E, 
draw  horizontal  lines  to  meet  the  perpendiculars  from  i,  2,  3, 
4,  &c.,  and  the  intersection  of  these  lines  are  the  points 
through  which  the  theoretical  curve  must  pass.  This  method, 
(as  well  as  all  others),  of  constructing  the  hyperbolic  curve  is 
based  on  the  assumption  that  the  temperature  of  the  steam, 
(or  other  medium)  remains  the  same  throughout  its  range  of 
movement ;  and  also  that  the  piston  and  valves  are  absolutely 
tight,  as  well  as  an  absence  of  condensation,  or  any  other  dis- 
turbing influences. 

It  is  well  known  in  indicator  practice,  that  in  taking  dia- 
grams from  *a  steam  engine  cylinder,  we  are  subjected  (at  times) 
to  all  of  the  influences  here  mentioned.  The  temperature  of 
the  steam  changes  during  the  stroke,  and  usually  we  find  the 
piston  and  valves,  more  or  less  leaky ;  also  initial  condensation 
and  re-evaporation  takes  place,  (to  a  certain  extent)  all  combin- 
ing to  cause  a  departure  of  the  actual  (more  or  less)  from  the 
true  theoretical  curve.  Therefore  one  of  the  objects,  in  con- 
structing the  theoretical  curve,  is  for  the  purpose  of  comparing 
and  ascertaining  the  extent  of  this  departure,  where  princi- 
pally located ;  to  study  and  find  the  cause  of  any  discrepancies, 
so  as  to  enable  the  engineer  to  apply  the  necessary  means  to 
correct,  as  nearly  as  possible,  any  disagreements  that  may  ap- 
pear in  the  actual  curve. 

In  the  construction  of  the  theoretical  curve,  it  has  been 
assumed  that  the  temperature  of  the  steam  remains  the  same 


A  nd  Its  Appliances.  1 03 

throughout  the  stroke ;  whereas  the  temperature  of  the  steam 
in  an  engine  cylinder,  gradually  decreases  from  point  of  cut-off 
to  the  end  of  expansion.  Hence,  (all  other  conditions  being 
perfect)  temperature  alone  would  result  in  a  slight  disagreement, 
and  cause  the  actual  curve  at  its  terminal  (with  a  given  cut-off) 
to  be  a  little  below  the  theoretical.  The  re-evaporation  of  the 
steam  condensed  in  the  earlier  part  of  the  stroke,  however, 
will  later  on,  tend  in  a  measure,  to  increase  the  pressure,  there- 
by raising  the  actual  expansion  line  to  more  nearly  conform 
with  the  theoretical  curve ;  therefore  as  a  general  thing,  a 
close  approximation  of  the  actual  expansion  curve,  with  the 
theoretical,  may  be  taken  as  evidence  of  correct  valve  adjust- 
ment, and  good  practice.  It  is  always  advantageous  to  draw 
the  true  theoretical  line  on  the  diagram,  in  order  that  the  ac- 
tual line  may  be  compared  with  it. 


IO4  Steam  Engine  Indicator 


CHAPTER  XV. 


ADIABATIC   CURVE   AND    POINT    OF   CUT-OFF. 


The  curve  formed  in  accordance  with  the  principles  of  the 
Mariotte  law,  depends  for  its  correctness  upon  the  condition 
that  the  temperature  of  the  steam  in  the  cylinder  remains  the 
same  during  the  entire  stroke ;  and  the  curve  that  coincides 
with  this  law  of  expansion,  is  the  Hyperbolic  or  Isothermal, 
in  which  it  is  assumed  that  the  steam  within  a  cylinder  during 
expansion  is  of  exactly  the  same  temperature  throughout  the 
length  of  the  diagram ;  whereas  the  pressure  from  the  point 
of  cut-off,  to  the  end,  is  continually  changing,  and  any  change 
in  the  pressure  of  steam,  is  always  accompanied  by  a  change 
of  temperature ;  therefore  the  application  of  this  law  to  a  dia- 
gram from  a  steam  cylinder,  would  not  be  absolutely  correct, 
because  for  any  change  in  volume  of  the  steam,  the  corres- 
ponding change  that  takes  place  in  pressure,  would  be  more 
than  if  the  temperature  had  remained  constant ;  or  more,  than 
of  a  curve  constructed  in  accordance  with  the  Mariotte  law.  A 
method  of  improving  this  condition  of  temperature,  and  pres- 
sure, is  by  means  of  a  steam  jacket  surrounding  the  cylinder, 
for  transmitting  heat  from  said  jacket  to  the  steam  within  the 
cylinder  during  expansion ;  and  thereby  in  a  measure  supply- 
ing the  necessary  heat  for  re-evaporation,  and  also  for  increas- 
ing the  temperature,  and  consequently  the  pressure,  thereby 
raising  the  actual  line  of  diagram,  in  the  latter  part  of  the 


And  Its  Appliances. 


105 


A.B.C.- 


stroke  and  thus  causing  it  to  very  nearly  conform  to  the  Isoth- 
ermal or  theoretical  curve. 

In  case  of  exposed  cylinders,  or  where  no  provision  is 
made  for  transmitting  heat  to  the  steam  during  the  stroke,  a 
curve  may  be  drawn  approximately,  representing  this  curve  of 
actual  conditions;  wherein,  all  changes  of  volume  and  tem- 
perature are  accompanied  by  a  change  of  pressure.  This  curve 
is  called  the  Adiabatic ;  as  shown  in  Fig.  57,  and  may  be,  in  fact, 
considered  the  true  theoretical  curve,  and  more  nearly  corres- 
ponding to  the  actual  change  of  pressure  that  takes  place,  dur- 
ing expansion  in  an  unjacketed  steam  cylinder.  We  are  not 

aware  of  an  absolutely 
correct  method  of  con- 
structing the  Adiabatic 
curve;  which  term 
means,  that  when  steam 
or  other  medium  is  un- 
der either  expansion  or 
compression,  no  heat 
enters  or  leaves  it  dur- 
ing that  time.  An  ap- 
proximate curve  may 
be  drawn  with  the  aid 
FIG.  57.  of  a  table  of  the  prop- 

erties of  saturated  steam ;  although  in  most  cases  the  consid- 
eration of  this  curve  is  more  a  problem  for  experts,  than  for 
the  average  engineer. 

Diagram  Fig.  57,  is  presented  to  show  the  difference  be- 
tween the  two  theoretical  curves,  as  compared  with  the  actual 
line  of  the  diagram.  The  upper  full  line  T,  C,  is  the  adiaba- 
tic, and  T,  B,  shown  in  dotted  lines,  is  the  isothermal  curve ; 
while  the  lower  full  line  T,  A,  represents  the  line  described 
by  the  indicator.  If  the  top,  (instead  of  the  terminal)  of  the 
curve  T,  C,  had  been  made  to  coincide  with  the  theoretical 
point  of  cut-off  B,  the  adiabatic  would  have  fallen  about  two 


io6  Steam  Engine  Indicator 

pounds  per  square  inch  below  the  theoretical  curve  at  the  ter- 
minal. I 

In  almost  all  diagrams  however, 'from  engines  having  tight 
pistons  and  valves,  with  properly  jacketed  cylinders,  and 
wherever  a  high  mean  effective  pressure,  with  a  low  terminal 
is  obtained,  thereby  securing  good  efficiency  and  economy ;  it 
is  found  in  all  such  cases  that  the  actual  curve  produced  by  the 
indicator,  conforms  very  nearly  with  the  Isothermal  or  theoret- 
ical curve.  The  fact  of  such  agreement  therefore  must  be  due  to 
a  transmission  of  heat  to  the  steam  in  the  cylinder  during  expan- 
sion ;  thus  increasing  the  temperature  and  thereby  producing  a 
re-evaporation  of  a  part  of  the  steam  condensed  in  the  earlier  part 
of  the  stroke.  As  the  isothermal  curve  is  very  easily  drawn 
and  apparently  correct  enough  for  all  practical  purposes,  it  is 
therefore  the  curve  now  almost  universally  used  by  all  classes 
of  engineers,  for  the  purpose  of  comparing  with  it,  the  lines 
of  the  actual  diagram ;  and  where  any  considerable  departure 
is  found  in  the  actual  curve,  all  efforts  are  directed  toward 
making  such  changes  in  the  valve,  and  piston  mechanism,  as 
may  be  necessary  to  produce  uniformity  and  a  close  coin- 
cidence of  the  actual  line  with  the  isothermal,  and  where  they 
do  so  agree  is  generally  considered  an  evidence  of  correct 
valve  adjustment  and  efficiency  of  the  engine.  This  presump- 
tion is  no  doubt  nearly  correct  in  most  cases,  with  steam 
jacketed  cylinders,  and  where  the  piston  and  valves  are  tight ; 
but  a  close  agreement  must  not  always  be  taken  as  conclusive 
evidence  of  economical  results;  as  we  often  find  in  practice 
some  actual  diagrams  that  coincide  very  nearly  with  the  the- 
oretical ;  but  still  upon  investigation  of  the  amount  of  steam 
used  in  the  engine,  they  will  be  found  to  be  deceptive  and  the 
opposite  of  economical  conditions. 

This  deception  in  many  cases  arises  from  a  leaky  condition 
of  the  piston  and  valves,  rather  than  from  any  lack  of  proper 
adjustment  in  the  timing  of  these  parts;  therefore  any 


And  Its  Appliances.  107 

decided  disagreement  of  the  actual  curve  from  isothermal,  gen- 
erally indicates  a  leakage  of  steam,  either  through  the  valves 
or  piston  or  both ;  and  these  may  enter  into  combination,  in  such 
a  manner,  as  to  be  very  misleading.  The  consequences  of  a 
leaky  steam  valve  are  that  it  will  always  cause  the  actual 
curve  of  the  diagram  to  be  higher  than  it  should  be  at  the 
terminal  from  a  given  cut-off,  The  actual  curve  in  Fig.  57, 
represents  the  effect  on  the  diagram  of  a  leaky  steam  valve. 
In  this  case  the  Isothermal  (shown  in  dotted  lines),  has  been 
started  at  the  end  of  the  expansion,  for  the  purpose  of  showing 
how  much  more  work  might  have  been  done  by  the  steam, 
from  the  given  terminal ;  whereas  if  it  had  been  drawn  to  coin- 
cide at  the  commencement,  with  the  absolute  point  of  cut-off, 
(that  is,  at  the  intersection  of  the  actual  curve  with  the  line 
D,  B,)  it  would  have  shown  the  expansion  line  of  said  curve 
considerably  higher  than  the  theoretical  at  the  terminal  T; 
this  being  due  to  the  extra  amount  of  steam  entrained  through 
the  valve  after  cut-off  and  during  expansion. 

If,  in  the  present  instance  the  piston  had  leaked  just  suf- 
ficient to  cause  the  expansion  line  to  coincide  with  the  theoret- 
ical ;  then  the  diagram  might  have  been  considered  from  obser- 
vation alone;  as  representing  economy  and  good  conditions  in 
the  engine ;  when  in  fact  the  reverse  of  this  is  the  case,  owing 
to  leaky  condition  of  both  of  the  parts  named.  Therefore  in 
order  to  secure  the  most  economical  results  in  the  steam  en- 
gine, it  is  of  the  first  importance,  and  absolutely  necessary 
that  the  valves  and  piston,  be  practically  tight,  in  order  that 
all  losses  arising  from  this  source  shall  be  brought  to  a  mini- 
munio  A  leaky  steam  valve  will  be  less  noticeable  at  the  com- 
mencement, or  in  the  earlier  part  of  expansion,  because  of  the 
slight  difference  of  pressure  at  that  part  of  the  stroke,  between 
the  steam  in  the  cylinder  and  that  in  the  steam  chest,  but  will 
become  more  apparent  on  the  expansion  line,  as  these  pres- 
sures become  more  unbalanced  in  the  latter  part  of  the  stroke. 


io8  Steam  Engine  Indicator 

Also  a  leaky  piston  will  be  indicated  by  a  sudden  falling  away 
of  the  actual  curve  from  the  theoretical  at  the  beginning  of 
expansion,  due  to  the  difference  in  pressure  between  the 
opposite  sides  of  the  piston,  but  as  the  pressures  become  more 
equalized  later  in  the  stroke,  this  difference  will  finally  dis- 
appear. If  the  valves  and  piston  are  absolutely  tight,  (thereby 
obviating  all  leakage)  and  also,  if  no  re-evaporation  takes 
place,  then  the  theoretical  curve  drawn  strictly  in  accordance 
with  the  principles  of  the  Mariotte  law,  must  necessarily  be,  at 
the  point  of  release  (from  a  given  cut-off),  higher  than  the  ac- 
tual curve,  principally  on  account  of  the  increasing  volume  of 
the  steam,  thereby  diminishing  its  heat,  and  consequently  its 
pressure  during  expansion.  But  in  indicator  practice  the  re- 
verse of  this  is  usually  found,  and  in  most  cases  the  actual 
curve  will  be  above  the  theoretical  at  the  point  of  exhaust  open- 
ing. This  evident  rise  of  pressure,  in  the  latter  part  of  the 
stroke,  is  claimed  by  some  engineers  to  be  due  to  a  re-evapor- 
ation of  the  steam,  that  has  lost  a  portion  of  its  heat,  and 
therefore  condensed,  by  contact  with  the  colder  surface  of 
the  cylinder  at  the  commencement  and  earlier  part  of  the 
stroke ;  said  heat  being  again  restored  in  the  latter  part  of  the 
stroke  by  transmission  from  the  inner  surface  of  the  cylinder. 

It  is  construed  by  others  to  be  due,  more  to  defective  and 
leaky  steam  valves  than  to  re-evaporation.  It  may  be  due 
either  to  the  latter,  or  to  a  leaky  steam  valve,  or  both  com- 
bined, and  therefore  becomes  a  matter  for  consideration  and 
judgment  in  most  cases  on  the  part  of  the  engineer. 

The  rise  in  pressure  from  re-evaporation  alone,  would  hardly 
cause  the  actual  line  to  go  much,  if  any,  above  the  theoretical; 
consequently  a  close  agreement  of  the  actual  line  of  the  dia- 
gram to  this  line,  is  all  that  can  be  expected,  or  desired  under 
the  circumstances. 

The  location  of  the  correct  point  of  cut-off,  on  the  diagram 
is  another  matter  that  requires  considerable  experience  and 


A  nd  Its  Appliances. 


109 


judgment  in  selecting  the  best  point  on  the  actual  curve,  to  be 
used  as  a  basis,  with  any  of  the  various  geometrical  methods  of 
construction,  employed  for  locating  the  correct  point  of  cut-off ; 
all  of  which  give  about  the  same  results. 

One  method  of  con- 
struction for  locating 
the  point,  is  repre- 
sented in  Fig.  58,  as 
follows:  Draw  the 
vacuum  line  V,  Vi, 
parallel  and  below  the 
atmospheric  H,  I,  at 
a  distance  equal  to 
14.7  pounds  by  the 
scale  of  the  spring. 
1r/  Draw  the  line  A,  E, 
also  parallel  and  just 
the  diagram.  The  clearance 


top  of 


FIG.  58. 

touching,  or  near  the 
being  known,  or  de- 
termined by  either  of 
the  methods  previous- 
ly described  erect  the 
clearance  line  K,  ac- 
cordingly ;  select  any 
point  on  the  expansion 
line,  where  it  is  known 
that  the  steam  and 
exhaust  valves  are 
closed,  as  at  D,  and 
erect  a  perpendicular, 
intersecting  the  line 
A,  E,  at  B;  from  B, 
draw  the  diagonal 
line  to  to  the  vacuum  point  V,  and  from  D,  draw  a  horizontal 


FIG.  59. 


no 


Steam  Engine  Indicator 


line  cutting  the  diagonal  B,  V,  at  F.  From  F,  erect  a  perpen- 
dicular intersecting  the  line  A,  E,  at  C.  ThenC,  is  the  correct 
point  of  cut-oif ;  or  is  where  the  further  admission  of  steam  to 
the  cylinder  must  be  stopped,  in  order  that  the  expansion  line 
shall  pass  through  the  selected  point  D.  This  diagram  is  rep- 
resented as  having  been  taken  from  a  single  cylinder  condens- 
ing engine,  the  steam  valve  having  no  apparent  leakage,  and 
the  point  D,  as  being  selected  below  the  atmospheric  line. 

The  diagram  represented  in  Fig.  59,  is  taken  from  the 
same  style  of  engine  as  Fig.  58  and  the  method  of  locating  the 
point  of  cut-off  is  precisely  the  same.  The  only  difference  be- 
tween the  diagrams,  being  in  the  location  of  the  point  selected 
on  the  expansion  line.  Here  the  point  D  is  nearer  the  center 
of  the  curve,  and  above  the  atmospheric  line,  and  gives  the 
correct  point  of  cut-off  at  C.  The  construction  of  the  theor- 
etical curve  on  the  diagram,  in  this  case,  indicates  a  consider- 
able leak  in  the  steam  valve.  It  is  not  necessary  that  the  line 

A,  E,  be  drawn  at  the 
extreme  top,  as  in  dia- 
grams where  the  valve 
is  slow  in  closing,  and 
thereby  causing  the 
curve  of  cut-off  to  be  de- 
cidedly rounded,  it  may 
be  better  to  draw  the 
line  through  the  abso- 
lute closure,  as  near  as 
can  be  observed ;  in  or- 
der that  the  contrast 
may  be  more  plain  at 
FIG.  60.  that  point. 

Another  very  simple  method  of  locating  the  point  of  cut- 
off, is  represented  in  Fig.  60,  and  is  as  follows:  Draw  the 
vacuum  and  clearance  lines  the  same  as  in  the  preceding 


A  nd  Its  A  ppliances,  v  r  / 

figures ;  also  the  line  A,  E,  near  the  top,  or  through  the  noted 
point  of  cut-off.  From  V,  draw  the  diagonal  line  at  an  angle 
of  45  degrees,  with  the  vacuum  line,  and  intersecting  the  line 
A,  E,  at  B,  drop  a  line  from  B,  cutting  the  expansion  line  at 
D.  Place  one  point  of  a  pair  of  dividers  at  B,  and  with  a 
radius  equal  to  B,  D,  describe  the  arc  D,  C,  cutting  A,  E,-at 
C,  then  C  will  be  the  correct  cut-off  point.  The  drawing  of 
the  diagonal  line  will  be  more  quickly  done  by  the  use  of  a  45 
degree  triangle,  but  in  the  absence  of  one,  may  be  done  by 
the  method  as  shown  in  Fig.  60.  Place  one  point  of  the  divid- 
ers at  V,  and  with  any  convenient  radius  describe  the  arc  1,2; 
then  with  the  same  radius,  and  from  i  and  2,  draw  short  arcs, 
cutting  each  other  at  the  point  3.  From  V,  draw  the  diagonal 
through  the  intersection  at  3,  which  will  be  the  desired  angle. 


Vi2  Steam  Engine  Indicator 


CHAPTER  XVI. 


THE   FOOT-POUND,    AND    MEASUREMENT   OF   DIAGRAMS. 


The  foot  pound  is  the  unit  of  measurement  in  computing 
the  power  of  steam  engines  and  represents  the  work  required 
to  lift  one  pound,  one  foot  high.  The  established  standard  of 
horse-power  being  33,000  foot  pounds  or  an  equivalent  amount 
of  work,  such  as  1000  pounds  lifted  33  feet;  500  pounds  66 
feet;  or  100  pounds  lifted  330  feet  in  one  minute.  The  horse 
power  of  a  steam  engine  is  therefore  denoted  by  the  number 
of  pounds  it  is  capable  of  raising  to  a  given  height  in  one  min- 
ute. The  usual  and  correct  method  of  computing  this  is  by 
multiplying  the  area  of  the  piston  (in  square  inches),  by  the 
mean  effective  pressure  of  the  steam  acting  against  the  piston 
throughout  the  stroke,  and  also  by  the  speed  of  the  piston 
(in  feet),  per  minute,  and  dividing  the  product  of  such  multi- 
plication by  33,000,  the  quotient  will  be  the  indicated  horse- 
power. 

For  instance:  Suppose  we  have  an  engine  in  which  the 
piston  area  is  201  square  inches,  with  a  mean  effective  pressure 
of  30  pounds  per  square  inch,  and  a  piston  speed  of  450  feet 

per  minute,  then ^-  =  82.22+  indicated  horse-power. 

33,000 

The  actual  efficient  horse-power  will  be  somewhat  less ;  de- 
pending upon  the  amount  of  friction  in  the  engine.  A  ready 
and  convenient  method  of  calculating  the  horse-power  from  a 


And  Its  Appliances.  113 

number  of  cards  from  the  same  engine,  is  for  the  engineer  to 
first  compute  the  horse-power  of  his  engine  at  one  pound  mean 
effective  pressure  and  using  the  number  so  found  as  a  constant 
or  multiplier  for  all  other  mean  effective  pressures.  For  illus- 
tration :  Suppose  as  in  the  preceding  example,  the  piston  area 
to  be  201  square  inches,  and  piston  speed  450  feet  per  minute, 

then  45   =  2 . 74+  which  is  the  horse-power  of  the  engine 

33,000 

at  one  pound  mean  effective  pressure, and  which  may  be  used 
as  a  multiplier  for  all  other  mean  effective  pressures  in  the  en- 
gine ;  the  product  of  the  multiplication  will  be  the  total 
indicated  horse-power.  Hence  the  horse-power  of  the  engine 
at  one  pound  mean  effective  pressure  as  above  being  2.744- 
therefore  at  30  pounds  it  will  be  30X2.74=82.20,  or  at  25 
pounds  mean  effective  pressure  would  be  25x2.74=68.50  in- 
dicated horse-power.  The  factors  connected  with  the  subject 
are  therefore,  as  before  stated,  ist.  The  area  of  the  piston 
(in  square  inches),  which  can  be  obtained  from  a  table  of  the 
diameters  and  areas  of  circles,  or  may  be  computed  by  multi- 
plying the  square  of  the  diameter  in  inches  by  the  decimal 
.7854;  the  product  will  be  in  square  inches.  2nd.  The  speed 
of  the  piston  (in  feet),  per  minute  and  which  may  be  found  by 
multiplying  twice  the  length  of  the  stroke  (in  feet),  by  the 
number  of  revolutions  of  the  crank,  which  will  give  the  piston 
speed  in  feet  per  minute.  3rd.  The  force  or  mean  effective 
pressure  of  the  steam,  acting  upon  the  piston  during  the  time. 
The  product  of  all  three  being  divided  by  33,000,  the  standard 
unit  of  horse-power. 

The  indicator  in  most  cases  is  used  principally  for  deter- 
mining the  horse-power ;  but  by  the  aid  of  its  record  made  on 
the  card,  the  impelling  force  against  the  piston  at  all  periods 
of  the  stroke,  is  made  visible,  and  thereby  furnishes  an  index 
of  the  work  performed,  and  enables  the  engineer  to  study  in- 
telligently many  other  important  matters  connected  with  the 


Steam  Engine   Indicator 


ro. 


problem  of  steam  economy.  In  order  to  determine  the  horse- 
power of  an  engine,  it  first  becomes  necessary  to  ascertain  from 
the  diagram,  the  mean  effective  pressure  of  the  steam  acting 
upon  the  piston  during  the  stroke  of  the  engine.  The  finding 
of  the  mean  effective  pressure  is  rapidly  and  easily  accom- 
plished by  the  use  of  the  Planimeter,  an  instrument  especially 
adapted  for  the  purpose ;  but  when  an  instrument  of  this  kind 
is  not  at  hand,  this  pressure  may  be  approximately  determined 
by  means  of  a  number  of  lines  drawn  through  the  diagram  as 

represented  in  Fig.  61, 
and  is  as  follows:  Di- 
vide the  diagram  into 
any  number  of  equal 
parts,  and  draw  lines 
(called  ordinates), 
through  each  division 
and  perpendicular  to 
the  atmospheric  line ; 
thus  dividing  the  dia- 
gram into  a  number  of 
small  areas.  The  mean 
effective  pressure  may 
now  be  found  by  meas- 
uring the  height  of 
each  line,  in  pounds,  by  a  scale  corresponding  with  the  scale  of 
the  spring  with  which  the  diagram  was  taken  ;  then  by  adding 
the  pressures  so  found  at  each  division  and  dividing  their  com- 
bined sum  by  the  number  of  divisions  into  which  the  diagram 
has  been  divided,  will  give  the  mean  effective  pressure  in 
pounds  per  square  inch.  The  diagram,  Fig.  61,  is  shown  (by 
the  ordinates  in  full  line),  to  be  divided  into  ten  equal  parts; 
consequently  ten  would  be  the  divisor  for  the  combined  sum 
of  the  ordinates  in  this  case;  for  example:  The  combined 
length  of  the  ordinates  measured  in  pounds  by  the  scale  of  the 


FIG.  61. 


And  Its  Appliances.  115 

spring  (50)  is  428  and  this  divided  by  the  number  of  divisions 
as  42  8 -f- 10=42.8  pounds  mean  effective  pressure. 

Where  greater  accuracy  is  desired,  or  where  the  outlines 
of  the  diagram  are  very  irregular,  it  may  be  advisable  to  sub- 
divide as  shown  in  dotted  lines,  making  twenty  divisions,  and 
consequently  dividing  their  combined  sum  by  twenty.  In  dia- 
grams where  this  irregularity  exists  only  in  a  part  of  its 
length,  it  is  sufficient  (at  that  part  alone),  to  sub-divide  on  each 
side  of  the  line  or  lines,  for  which  the  pressure  is  required; 
and  measure  the  pressure  on  each  sub-division ;  add  together 
and  divide  their  sum  by  two  (2) ;  the  quotient  will  be  the  pres- 
sure sought  on  the  full  division  line  as  shown  at  the  top  of  the 
diagram  in  Fig.  61. 

In  place  of  measuring  the  heights  of  the  ordinates,  (in 
pounds)  by  the  scale  of  the  spring,  each  may  just  as  well  be 
measured  in  inches.  If  the  sum  of  their  combined  length  be 
multiplied  by  the  scale  of  the  spring,  and  divided  by  the  num- 
ber of  ordinates,  the  quotient  will  be  the  mean  effective  pres- 
sure in  pounds  per  square  inch,  acting  against  the  piston 
throughout  the  stroke.  For  example :  The  combined  length'  of 
the  ordinates  measured  -in  inches  is  8.56,  then  8.56x50-^-10= 
42.8  pounds  mean  effective  pressure,  the  same  as  before.  An- 
other convenient  method,  which  has  the  merit  of  simplicity 
may  be  staten  as  follows :  If  we  draw  the  number  of  ordinates 
in  the  length  of  the  diagram  equal  to  the  number  correspond- 
ing with  the  denomination  of  the  spring,  then  the  combined 
length  of  the  ordinates  in  incJies  will  be  the  mean  effective 
pressure  in  pounds  per  square  inch.  For  example  :  Suppose  in 
the  diagram,  Fig.  61,  the  spring  to  be  a  50  and  that  the  length 
of  the  diagram  be  divided  into  the  same  number  (50)  of  equal 
parts,  then  each  inch  of  the  combined  length  of  the  ordinates 
would  represent  one  pound  mean  effective  pressure.  If  it  had 
been  divided  into  twenty-five  (25)  parts,  then  each  inch  would 
represent  two  (2)  pounds  mean  effective  pressure,  etc.,  and  in 


1 1 6  Steam  Engine  Indicator 

any  case  by  dividing  the  number  representing  the  denomina- 
tion of  the  spring  by  the  number  of  division  in  the  length  of  the 
diagram ;  the  quotient  will  be  the  multiplier  for  the  combined 
length  of  the  ordinates  in  inches,  and  the  product  of  such  mul- 
tiplication will  be  in  pounds  mean  effective  pressure.  For  in- 
stance :  The  combined  length  of  the  ten  divisions  in  the  dia- 
gram, Fig.  61,  is  8.56  inches,  and  the  scale  of  the  spring  is  50, 
therefore  50-^-10=5  and  8.56x5  =  42.8  pounds  mean  effective 
pressure,  the  result  being  precisely  the  same  as  by  the  other 
methods.  In  working  out  the  diagrams  it  is  advisable  to  make 
the  divisions  as  numerous  as  convenient,  which  tends  to  more 
accurate  results,  and  particularly  so  where  the  outline  of  the 
diagram  is  very  irregular. 

In  cases  where  a  scale  of  the  spring  is  not  at  hand,  a  con- 
venient method  of  finding  the  combined  length  of  the  ordinates 
is  by  taking  a  narrow  strip  of  paper  and  marking  on  it  the 
height  of  each  division,  commencing  at  No.  i.  Mark  its 
length  on  the  paper,  then  place  the  mark  made  at  the  top  of 
No.  i  on  the  bottom  of  No.  2  and  mark  the  top  of  No.  2,  and 
so  on  successively  to  the  end  of  the  diagram,  then  measuring 
their  total  combined  length  in  inches  which  being  multiplied  by 
the  number  of  spring,  and  divided  by  the  number  of  divisions, 
will  give  the  mean  effective  pressure,  in  pounds,  per  -square 
inch,  or,  in  place  of  measuring  with  a  strip  of  paper,  it  may  be 
as  correctly  done  by  drawing  a  straight  line  of  sufficient  length 
to  contain  the  combined  length  of  the  ordinates,  and  with  a 
pair  of  dividers  set  to  the  length  of  each  different  ordinate  suc- 
cessively; commencing  at  No.  i,  and  transferring  the  length 
of  each  upon  the  line.  The  mean  effective  pressure  may  then  be 
found  from  the  total  length  in  inches  after  all  the  measurements 
of  the  ordinates  have  been  transferred  to  the  line,  by  either  of 
the  two  latter  methods  of  computation. 

The  diagram,  Fig.  62,  represents  the  effect  in  a  non-con- 
densing engine  of  cutting  off  the  steam  at  a  very  early  part  of 


And  Its  Appliances.  117 

the  stroke,  and  shows  the  expansion  line  crossing  and  running 
below  the  atmospheric  line  for  the.  greater  part  of  the  stroke. 
This  result  is  a  general  thing  brought  about  in  diagrams  from 
an  engine  having  insufficient  load.  In  this  case  the  diagram 
is  composed  of  two  distinct  parts,  and  must  be  treated  as  such 
in  computing  the  horse-power  of  the  engine. 

In  Fig.  62,  all  ordi- 
nates  above  the  atmos- 
pheric line,  and  to  the 
left  of  where  the  expan- 
sion  crosses  the  back 
pressure  line,  will  rep- 
resent  positive  pressure, 

\  and  all  ordinates  to  the 

right  of  the  above,  and 


. 
V 


|Sv 


IV  between  the  back  pres- 


i^lj  I  I  I  I  I  I  I  Tfr  sure  an(^  boundary 
line  of  the  diagram, 
will  be  negative,  and 


FIG.  62.  the  combined   length 

of  the  latter  must  be  deducted  from  the  former,  in  order  to  as- 
certain the  mean  effective  pressure.  For  example :  Suppose 
the  scale  of  the  spring  to  be  40,  and  the  combined  length  of 
the  ordinates  of  positive  pressure  to  be  4.05  inches  while  the 
combined  length  of  the  lines  of  negative  pressure  is  1.65 
inches,  then  the  difference  will  be  4.05—1.65  =  2.4  inches. 
The  number  of  divisions  of  the  diagram  (20)  being  just  one- 
half  of  the  scale  of  the  spring  (40),  it  is  only  necessary  to  mul- 
tiply the  difference  in  the  length  of  the  lines  by  two ;  that  is 
2.4x2  =  4.8  pounds  mean  effective  pressure  throughout  the 
stroke.  An  indicator  diagram  like  Fig.  62  always  indicates  a 
loss  of  efficiency  and  measures  should  at  once  be  taken  to  rem- 
edy the  evil. 

In  the  matter  of  the  computation  of  diagrams  for  mean 
effective   pressure   alone,    it   may   here  be  well   to  state,  that 


n8 


Steam  Engine  Indicator 


neither  the  atmospheric,  vacuum,  or  clearance  lines  become 
factors  in  the  case ;  therefore  we  have  only  to  deal  with  the 
lengths  of  ordinates  within  the  actual  boundary  line  of  the 
diagram. 


And  Its  Appliances.  lip 


CHAPTER  XVII. 


EXPANSION   OF    STEAM. 


The  expansion  of  steam  in  the  cylinder  of  an  engine  per- 
forming work  coincides  very  nearly  with  the  principle  of  the 
law  pertaining  to  gases,  and  known  as  the  Mariotte  law ;  (as 
before  noted  in  Chapter  XIV)  wherein  the  pressure  varies  in- 
versely as  the  volume ;  the  temperature  remaining  the  same. 

Upon  opening  communication  (at  any  observed  pressure 
of  steam)  between  a  boiler,  and  the  cylinder  of  a  steam  engine, 
a  corresponding  pressure  of  steam  will  be  exerted  against  the 
piston,  and  unless  the  steam  be  either  condensed,  or  discharged 
from  the  cylinder,  the  same  pressure  will  continue  to  act  upon 
the  piston  ;  even  after  the  valve  has  been  closed  that  commun- 
icates with  the  boiler,  and  this  pressure  will  continue  so  long 
as  the  volume  and  temperature  remains  unchanged. 

If  steam  is  supplied  from  a  boiler  to  move  a  piston  altern- 
ately in  a  cylinder,  and  the  valve  for  admission  of  steam  re- 
mains open  during  the  full  stroke  of  the  piston,  then  the 
cylinder  will  be  filled  with  steam  at  each  stroke  of  the  piston, 
of  a  pressure  nearly  equal  to  that  of  the  boiler ;  and  is  conse- 
quently exhausted  also  at  nearly  the  same  density. 

The  parallelogram  or  rectangle  shown  in  dotted  lines  b, 
d,  vi,  v,  of  Fig.  63  represents  a  theoretical  indicator  diagram 
from  a  condensing  engine  under  such  conditions;  the  line 


J20 


Steam  Engine  Indicator 


v,  vi  being  the  line  of  absolute  vacuum,  and  b,  d,  the  boiler 
pressure. 

Assume  an  indicator  to  be  attached  to  the  cylinder  of  such 
an  engine,  and  the  drum  carrying  the  paper  be  given  a  recip- 
rocating motion  to  coincide  (on  a  reduced  scale)  with  the  mo- 
tion of  the  engine  piston :  then  if  before  admitting  steam  to 
the  indicator  piston,  (and  while  the  drum  is  in  motion,)  the 


4 

£ 

• 

f 

& 

/^ 

X 

\ 

X 

K 

K 

a.r 

V 

y 

Tr' 

\*t 

4 

7                                     , 

< 

a 

? 

9 

FK 

s.  63. 

indicator  pencil  be  brought  in  contact,  with  the  drum,  a  hori- 
zontal line  a,  ai,  (called  the  atmospheric  line)  will  be  traced 
upon  the  paper;  in  length,  proportioned  to  the  stroke  of  the 
engine  piston ;  and  also  during  this  time,  the  pressure  of  the 
atmospheric  will  have  free  access  to  both  sides  of  the  indicator 
piston. 

If  communication  be  now  suddenly  opened  between  the 
steam  cylinder,  and  indicator,  at  a  time  when  the  pencil  is  at 
the  point  a,  the  pencil  will  ascend,  and  trace  upon  the  paper 


And  Its  Appliances.  12 1 

the  vertical  line  a,  b,  to  a  certain  height,  depending  upon  the 
pressure  of  the  steam,  and  also  upon  the  strength  or  scale  of 
the  indicator  spring  in  use ;  and  this  height  will  represent  the 
pressure  per  square  inch  of  the  steam  within  the  engine 
cylinder. 

Assuming  now  that  the  engine  piston  had  just  commenced 
to  move  from  left  to  right,  and  the  admission  of  steam,  con- 
tinues until  the  completion  of  the  stroke ;  the  pencil  will  have 
traced  the  line  b,  d,  representing  in  this  case  the  mean  pres- 
sure of  the  steam  throughout  the  stroke. 

If  at  the  point  d,  the  valve  for  the  admission  of  steam  be 
closed,  and  this  volume  of  steam  be  suddenly  condensed  by 
being  exhausted  into  the  condenser,  (thereby  creating  a  vac- 
uum) the  pencil  will  descend,  and  trace  the  line  d,  vi,  and 
consequently  on  the  return  stroke  follow  along  the  line  vi,  v, 
to  the  commencement;  thus  describing  a  parallelogram  of 
which  the  horizontal  line  v,  vi,  would  represent  the  length  of 
the  stroke  of  the  piston,  and  the  vertical  line  v,  b,  would  rep- 
resent the  total  steam  pressure  in  pounds  per  sqaure  inch  act- 
ing upon  the  piston ;  therefore  the  area  of  this  parallelogram 
would  represent  pounds  pressure,  multiplied  by  the  distance  in 
feet  moved  through  by  the  piston  in  a  single  stroke. 

The  theoretical  diagram  here  described  is  one  that  never 
occurs  absolutely  in  indicator  practice  ;  for  the  reason  that  the 
varying  circumstances  arising  in  the  use  of  steam,  would  always 
preclude  the  possibility  of  obtaining  such  a  result ;  therefore  it  is 
only  drawn  for  the  purpose  of  making  a  comparison  of  effi- 
ciency, between  it,  and  the  actual  diagram,  taken  as  near  as 
possible  under  the  same  conditions. 

In  the  foregoing,  steam  is  supposed  to  be  admitted  to  the 
cylinder,  during  the  entire  length  of  stroke  of  the  piston; 
without  any  attempt  to  employ  and  utilize  the  benefits  to  be 
derived  from  the  expansive  properties  of  the  steam. 


122 


Steam  Engine  Indicator 


The  diagram  in  full  line  of  the  same  figure,  show  approxi- 
mately the  outline  of  an  actual  diagram,  (in  practice)  as  the  re- 
sult of  such  an  adjustment  of  valves,  (as  herein  described)  as 
would  admit  steam  at  one  end,  and  exhaust  at  the  other,  alter- 
nately during  the  entire  length  of  each  stroke  of  the  piston. 

It  will  be  observed  that  the  actual  diagram  may  deviate  to 
a  considerable  extent,  from  the  theoretical,  in  accordance  with 
various  circumstances. 


1 

I 
0- 

V* 

HP 

x 

V 

> 

S 

'  I 

• 
' 

1 

1 

V 

i 

FIG.  64. 

For  instance,  the  boiler  pressure  may  not  be  fully  real- 
ized ;  also  the  interval  of  time  that  must  elapse  between  the 
point  of  commencement  of  opening,  or  closing  of  the  valves, 
and  the  absolute  accomplishment  of  the  same,  will  produce  a 
wire  drawing  effect  of  the  steam,  and  will  invariably  cause  the 
corners  of  the  diagram  to  be,  more  or  less,  rounded  off,  as 
shown  in  the  diagram. 

The  location  of  the  line  representing  the  back  pressure  on 
the  return  stroke,  will  depend  upon  the  degree  of  vacuum 


And  Its  Appliances.  123 

maintained  in  the  condenser,  and  this  will  usually  be  found  in 
most  diagrams,  to  be  from  three  to  five  pounds  above  the  line 
v,  vi,  of  absolute  vacuum. 

The  production  of  diagrams  like  the  one  shown  in  Fig.  63 
are  only  not  desirable,  but  the  reverse  of  economical,  and 
such  results  can  only  be  entertained  where  the  desire  is  to  ob- 
tain the  greatest  possible  power,  from  a  given  size  of  engine, 
without  regard  to  the  highest  economy. 

In  order  to  save  steam,  or  to  better  realize  the  econ- 
omy, and  efficiency  of  a  given  amount  of  steam  to  a 
greater  degree,  its  admission  to  the  cylinder  must  be  stop- 
ped, or  cut-off  after  the  piston  has  moved  only  a  portion  of 
the  stroke ;  and  as  the  piston  continues  to  move  along  the 
cylinder  (thereby  increasing  the  volume  of  the  steam  so  con- 
fined and  allowing  it  to  act  expansively),  its  pressure  from  the 
point  of  cut-off  will  gradually  diminish  to  the  end  of  the 
stroke,  and  in  such  proportion  as  corresponds  to  its  increased 
volume. 

Suppose  we  have  a  boiler  under  a  steam  pressure  of  60 
pounds  per  square  inch,  to  which  we  add  the  pressure  of  the 
atmosphere  (say  15  pounds),  making  a  total  of  60-1-15=75 
pounds  per  square  inch  absolute  pressure.  \ 

Now  if  this  steam  be  admitted  to  the  cylinder  of  an  engine, 
and  the  admission  stopped  after  the  piston  had  traveled  one- 
half  of  its  length  of  stroke,  as  represented  by  b,  c,  Fig.  64,  it 
will  have  performed  a  certain  amount  of  work,  which  may  be 
represented  in  foot-pounds ;  the  amount  being  the  product  of 
the  total  pressure  in  pounds  acting  upon  the  piston,  multi- 
plied by  the  distance  in  feet  it  has  passed  over. 

If  this  steam,  before  being  discharged  from  the  cylinder  is 
allowed  to  expand  to  double  its  volume,  thereby  forcing  the 
piston  to  the  end  of  the  stroke,  an  additional  amount  of  work 
will  have  been  performed  with  this  same  amount  of  steam,  and 


124  Steam  Engine  I e  die  at  or 

result  in  effecting  a  decided  economy  in  the  engine ;  as  this 
excess  of  work  has  been  obtained  through  utilizing  the  expan- 
sion of  the  steam. 

In  this  case  the  steam  was  expanded  to  twice  its  volume  at 
the  termination  of  the  stroke  of  the  piston,  with  a  pressure  of 
37 1/2  pounds  per  square  inch,  or  just  one-half  what  it  was  at 
half  stroke. 

In  Fig.  64,  suppose  the  stroke  of  the  piston  to  be  4  feet 
and  this  length  divided  into  eight  equal  parts,  i,  2,  3,  etc., 
each  part  or  volume  representing  six  inches,  or  one-half  foot 
of  the  stroke ;  then  if  the  piston  be  acted  upon  by  an  absolute 
pressure  of  steam  (as  before  stated),  of  75  pounds  per  square 
inch  at  the  beginning,  and  continued  to  the  fourth  division, 
(as  at  c),  equal  to  one-half  of  the  stroke,  it  will  have  performed 
an  amount  of  work  which  may  be  represented  by  the  mean 
pressure  (75  pounds)  multiplied  by  4,  (75X4)=3OO  foot  pounds 
of  work  for  each  square  inch  of  the  area  of  the  piston. 

If  the  admission  of  steam  be  stopped  or  cut-off,  after  the 
piston  has  arrived  at  half  stroke,  this  volume  of  steam  in  the 
cylinder  will  expand ;  and  its  pressure  will  gradually  diminish 
to  the  end  of  the  stroke ;  and  the  indicator  pencil  will  trace 
the  curve  line  c,  g,  and  when  the  exhaust  valve  opens  (assum- 
ing for  the  time  a  perfect  vacuum  in  the  condenser),  it  will  de- 
scend to  the  point  vi. 

In  the  diagram,  Fig.  64,  there  is  only  one-half  as  much 
steam  admitted  into  the  cylinder  during  the  stroke,  as  in  the 
case  of  diagram  Fig.  63,  but  it  will  be  readily  observed  by  a 
comparison  of  the  diagrams,  that  the  area  of  the  former  is 
greatly  in  excess  of  half  that  of  Fig.  63,  in  fact,  by  actual  com- 
putation, (the  rule  for  which  will  appear  later  on)  its  area  will 
be  found  to  be  about  .846  of  that  of  Fig.  63,  and  with  a 
mean  pressure  of  63.49  pounds  per  square  inch  during  the  en- 
tire stroke ;  (eight  divisions)  therefore  the  work  done  by  the 
steam  in  the  -  first-half  of  the  stroke  being  represented  by 


And  Its  Appliances. 


125 


75X4— 3OO>    the    amount    during   the   whole    stroke    will   be 

507.02 — 300     207.02       -  .     - 

63.49X  8=  507.92,  hence  — —     — - — =—      ^—=.093,  equivalent 

300  300 

to  a  gain  of  power  of  about  69.3  per  cent. 

This  has  been  obtained  through  utilizing  the  expansion  of 
half  the  quantity  of  steam  that  would  be  employed  during  the 
stroke  of  an  engine  represented  by  the  theoretical  diagram 
Fig.  63. 

6-  //  0L 


/  4.          J  •         4  ?          i  y  **> 

FIG.  65. 

Fig.  65  is  a  further  illustration  of  a  diagram  in  which  the 
admission  of  steam  is  cut  off  at  one-fourth,  and  expanded 
the  balance  of  the  stroke. 

In  this  case  the  amount  of  steam  used  is  only  one-fourth 
of  that  at  full  stroke,  but  the  total  area  of  the  diagram  is  over 
.58  of  the  full  theoretical  diagram;  and  which  is  equal  to  a 
mean  pressure  of  44. 74  pounds  per  square  inch  throughout  the 
entire  stroke,  (the  total  initial  pressure  as  stated  being  75 
pounds  per  square  inch.) 


126  Steam  Engine  Indicator 

Consequently  the  work  done  during  the  first  quarter  (one- 
fourth)  of  the  stroke  is  represented  by  75x2=  150,  and  during 

the  entire  stroke  by  44.74 X  8=357.92,  therefore  — 

_  =  1.38  equivalent  to  a  gain  of  138.  per  cent 

In  making  calculations  for  pressure  of  steam  after  it  has 
been  expanded,  it  is  the  total  pressure  that  must  be  considered, 
and  which  is  reckoned  from  absolute  vacuum. 

Consequently  the  extra  amount  of  force  thus  obtained,  and 
utilized  in  impelling  the  piston  the  balance  of  the  stroke,  may 
be  considered  theoretically  as  just  so  much  gain,  over  the  single 
effect  of  the  same  amount  of  steam ;  as  none  of  this  additional 
pressure  would  have  been  realized  upon  the  piston,  if  the 
stroke  had  terminated  at  the  point  where  the  steam  was  cut-off. 

From  this  theoretical  gain  however,  there  are  certain 
losses  that  must  be  deducted ;  such  as  friction  of  the  engine 
during  expansion  ;  the  loss  of  temperature  caused  by  the  grad- 
ual f  eduction  of  pressure  of  the  expanding  steam ;  and  this 
loss  is  further  increased  by  the  abstraction  of  heat  from  the 
cylinder  during  the  return  stroke ;  thereby  producing  a  com- 
paratively cooling  effect  on  the  interior  walls  of  the  cylinder 
and  also  the  piston. 

This,  as  a  consequence,  necessitates  a  greater  condensation 
of  the  steam,  (in  the  earlier  part  of  the  following  stroke)  be- 
fore the  temperature  of  the  cylinder  is  again  restored  to  that 
of  the  entering  or  initial  steam. 

In  practice  these  losses  prevent  the  full  theoretical  economy 
that  might  be  obtained  ;  therefore  in  order  that  the  maximum 
gain  from  expansion  may  be  realized,  they  must  be  reduced  to 
a  minimum. 

The  usual  means  employed  for  their  prevention,  is  by 
some  system  of  cylinder  covering  or  jacketing,  also  superheat- 
ing ;  to  obviate  the  matter  of  condensation ;  this  ajso  in 


And  Its  Appliances.  127 

connection  with  the  best  methods  of  reducing  the  friction  to  a 
minimum. 

The  economy  that  may  be  derived  from  the  expansion  of 
steam,  when  used  under  different  conditions,  is  an  import- 
tan  t  consideration,  and  requires  ability  and  good  judgment  (of 
the  engineer)  in  arriving  at  the  best  means  for  realizing  all 
expected  or  desired  results. 

The  greatest  gain  from  expansion  is  generally  secured 
in  Condensing  Engines,  but  the  application  of  a  condenser 
however  should  be  judiciously  made,  as  with  loads  already  too 
light,  it  would  be  of  little  value,  and  the  results  disappointing. 


«**  %. 


128  Steam  Engine  Indicator 


CHAPTER  XVIII 


HYPERBOLIC   LOGARITHMS. 


In  the  absence  of  an  indicator,  the  Mean  Effective  Pres- 
sure of  the  expanding  steam  in  a  cylinder,  and  the  power  of 
the  engine  from  a  given  pressure  of  steam,  and  point  of  cut-off 
may  be  approximately  ascertained,  and  the  average  pressure 
per  square  inch  that  will  be  exerted  against  the  engine  piston, 
during  the  stroke  can  be  estimated,  by  means  of  the  table  No. 
i,  of  Hyperbolic  Logarithms;  which  are  calculated  for  expan- 
sion according  to  the  Mariotte  law. 

The  Hyperbolic  Logarithm  as  found  in  the  table,  is  the 
product  of  the  common  logarithm  multiplied  by  2.302585  ;  and 
conversely  the  common  logarithm  is  the  product  of  the  hyper- 
bolic logarithm  multiplied  by  0.43429448. 

The  table  referred  to,  contains  the  hyperbolic  logarithm  of 
numbers  up  to  39,  which  are  considered  sufficient  for  applica- 
tion to  steam  expansion. 

The  rule,  and  method  of  calculating  the  Mean  Pressure  by 
the  use  of  the  table  is  as  f ollows : 

Rule.  To  the  total  length  of  the  stroke  of  the  engine  pis- 
ton, (in  inches)  add. the  clearance  in  the  cylinder  at  one  end 
(also  in  inches)  divide  this  sum  by  the  length  of  the  stroke  at 
which  the  steam  is  cut-off,  added  to  the  same  clearance ;  and  the 
quotient  will  express  the  ratio  or  number  of  expansions. 


And  Its  Appliances. 


129 


Find  in  the  table  the  logarithm  of  whatever  number  is 
nearest  to  that  of  the  quotient,  to  which  add  i. 

The  sum  is  the  ratio  of  the  gain. 

Multiply  the  ratio  thus  obtained  by  the  absolute  pressure 
of  steam  as  it  enters  the  cylinder,  and  divide  the  product  by  the 
relative  expansion ;  the  quotient  is  the  mean  pressure  required. 


No. 

Loga- 
rithms. 

No. 

Loga- 
rithms. 

No. 

Loga- 
rithms. 

No. 

Loga- 
rithms. 

0.0 

0.00000 

4.0 

1.38629 

7.0 

1.94591 

10 

2.30258 

1.1 

O.OJ530 

4.1 

1.41096 

7.1 

1.96006 

11 

2.39589 

1.2 

0.18213 

4.2 

.43505 

7.2 

1.97406 

12 

2.48491 

1.3 

0.26234 

43 

.45859 

7.3 

1.98787 

13 

2.56494 

1.4 

0.33646 

4.4 

.48161 

7.4 

2.00149 

14 

2.63906 

1.5 

0.40505 

4.5 

.50408 

7.5 

2.01490 

15 

2.70805 

1.6 

0.46998 

4.6 

.52603 

7.6 

2.02816 

16 

2.77259 

1.7 

0.53063 

4.7 

.54753 

7.7 

2.04115 

17 

2.83321 

1.8 

0.58776 

48 

.56859 

7.8 

2.05415 

18 

2.89037 

1.9 

0.64181 

4.9 

.58922 

7.9 

2.06690 

19 

2.94444 

2.0 

0.69315 

5.0 

.60944 

8.0 

2.07944 

20 

2.99573 

2.1 

0.74190 

5.1 

.62922 

8.1 

2.09190 

21 

3.04452 

2.2 

0.78843 

5.2 

.64865 

8.2 

2.10418 

22 

3.09104 

2.3 

0.83287 

5.3 

.66770 

8.3 

2.11632 

23 

3.13549 

2.4 

0.87544 

5.4 

.68633 

8.4 

2.12830 

24 

3.17805 

2.5 

0.91629 

5.5 

.70475 

8.5 

2.14007 

25 

3.21888 

2.6 

0.95548 

5.6 

.72276 

8.6 

2.15082 

26 

3.25810 

2.7 

0.99323 

5.7 

.74046 

8.7 

2.16338 

27 

3.29584 

2.8 

1.02962 

5.8 

.75785 

8.8 

2.17482 

28 

3.33220 

2.9 

1.06473 

5.9 

.77495 

8.9 

2.18615 

29 

3.36730 

3.0 

1.09861 

6.0 

.79175 

9.0 

2.19722 

30 

3.40120 

3.1 

1.13140 

6.1 

.80827 

9.1 

2.20837 

31 

3.43399 

3.2 

1.16314 

6.2 

.82545 

9.2 

2.21932 

32 

3.46574 

3.3 

1.19594 

6.3 

.84055 

9.3 

2.23014 

33 

3.49651 

3.4 

1.22373 

6.4 

.85629 

9.4 

2.24085 

34 

3.52636 

3.5 

1.25276 

6.5 

.87180 

9.5 

2.25129 

35 

3.55535 

3.6 

1  28090 

6.6 

1.88658 

9.6 

2.26191 

36 

3.58352 

3.7 

1.30834 

6.7 

1.90218 

9.7 

2.27228 

37 

3.61092  ' 

3.8 

1.33046 

6.8 

1.91689 

9.8 

2.28255 

38 

3.63759 

3.9 

1.36099 

6.9 

1.93149 

9.9 

2.29171 

39 

3.66356 

TABLE  No.  1. 


For  example.  Suppose  steam  of  100  pounds  absolute  pres- 
sure per  square  inch,  be  admitted  to  the  cylinder  of  an  engine, 
at  the  beginning  of  the  stroke  (ignoring  clearance  for  the 


130  Steam  Engine  Indicator 

present),  and  admission  stopped  after  one-fifth  (1-5)  of  the 
stroke  had  been  completed,  and  the  steam  allowed  to  gradually 
expand  to  the  end  of  the  stroke. 

Then  in  accordance  with  the  principle  of  the  law,  in  ref- 
erence to  the  expansion  of  gases,  the  volume  of  steam  in  this 
case,  on  being  continually  increased,  will  consequently  suffer 
a  corresponding  reduction  in  pressure. 

At  2-5  of  the  stroke  the  volume  will  be  double,  and  the 
pressure  reduced  to  l/2  of  the  initial,  or  to  50  pounds  per  square 
inch;  at  3-5  to  ^  or  33^  pounds;  at  4-5  to  J^  or  25  pounds, 
and  at  5-5  or  the  whole  stroke  the  volume  is  increased  5  times, 
with  a  reduction  of  pressure  of  1-5  initial  or  to  20  pounds  pres- 
sure per  square  inch  at  the  termination  of  the  stroke. 

Now  what  we  desire  to  ascertain  in  such  a  case,  is  the 
average  pressure  during  the  entire  stroke  or,  what  pressure 
acting  uniformally  throughout  the  stroke  will  perform  an 
equivalent  amount  of  work. 

This  may  be  calculated  very  readily  by  the  use  of  the 
Table  No.  i,  in  connection  with  the  Rule.  Suppose  in  the 
foregoing  example,  the  stroke  of  the  piston  to  be  60  inches, 
and  the  admission  of  steam  be  stopped  after  the  piston  had  ad- 
vanced 12  inches  and  expansion  continuing  to  the  end  of  the 
stroke ;  then  by  the  Rule  -ff  =  5  the  ratio  of  expansion. 

This  ratio  of  expansion  (5)  will  be  found  in  the  table  No. 
i,  under  the  head  of  numbers,  and  directly  opposite  (to  the 
right)  will  be  found  its  hyperbolic  logarithm  1.609,  to  which 
add  i.  the  sum  of  which  1.4-1.609=2.609  the  ratio  of  gain. 

Multiply  2.609  by  the  initial  pressure  of  steam  entering 
the  cylinder,  and  divide  the  product  by  (5)  the  ratio  of  expan- 

i.6ogX  100 
sion:  hence  -  —=$2.18  which  represents  in  pounds  per 

square  inch,  the  average  or  Mean  Pressure  that  would  be  ex- 
erted uniformally  against  the  piston  during  the  entire  stroke  of 
the  engine.  If  the  stroke  of  the  engine  piston  in  the  above 


A  nd  Its  Appliances.  131 

example  had  been  48  inches,  the  steam  cut-off,  after  the  piston 
had  advanced  12  inches,  and  the  absolute  initial  pressure  of 
the  entering-  steam  be  80  pounds  per  square  inch,  then  f|  =  4 
equal  the  ratio  of  expansion;  the  logarithm  of  which  is  1.386 
and  represents  the  ratio  of  the  gain. 

1.4-1.386x80     2.386X80 
Hence — • — — - —      ——47.72  which  would  ex- 

4  4 

press  the  Mean  Pressure  in  pounds  per  square  inch  impelling 
the  engine  piston  during  the  entire  stroke. 

In  computing  the  above  examples  for  the  Mean  Pressure, 
the  effect  of  the  clearance  in  the  cylinder,  has  been  purposely 
neglected,  in  order  that  the  calculation  might  be  presented  in 
a  more  simple  manner. 

In  the  case  of  the  latter  example,  suppose  the  percentage 
of  clearance  to  have  been  such  as  to  add  two  (2)  inches  in 
length  to  each  end  of  the  cylinder;  then  48+2=50  inches,  the 
length  of  stroke  with  the  clearance  at  one  end  added ;  and  by 
adding  the  same  clearance  to  the  distance  of  cut-off,  12+2=  14 
inches,  therefore  f£— 3-57  the  ratio  of  expansion  in  this  case. 

From  the  table  No.  i ,  we  find  the  nearest  number  to  this 
ratio  of  expansion  is  3.55  the  logarithm  of  which  is  1.267  to 

which  add  i.  then  i.+ 1.267= 2. 267  an(i  -  —=50.80  which 

o  •  j  / 

represents  the  Mean  Pressure  per  square  inch,  when  computed 
with  the  clearance  included,  instead  of  47.72  as  before;  an  in- 
crease of  3.08  pounds  per  square  inch. 

As  all  calculations  of  this  kind  are  generally  made  for  ap- 
proximate results  or  comparisons  only,  it  is  in  most  cases  un- 
necessary to  take  the  clearance  into  consideration,  unless  it 
should  be  unusually  large,  or  unless  the  cut-off  should  take 
place  very  early  in  the  stroke ;  either  of  which,  or  both  com- 
bined would  in  a  measure  cause  a  variation  in  the  final  re- 
sults. 


132 


Steam  Engine  Indicator 


This  indifference,  relative  to  the  clearance  in  the  calcula- 
tions proceeds  from  the  fact  that  the  full  boiler  pressure  is 
never  fully  realized  in  the  cylinder ;  and  also  on  account  of  a 
falling  of  pressure  that  often  takes  place  in  the  cylinder  before 
cut-off ;  and  it  may  be  assumed  that  what  will  be  gained  by 
clearance,  is  about  offset  by  the  failure  of  the  steam  to  fulfill  the 
conditions  required. 


Portion  of  stroke 
at  which 
steam  is  cut  off. 

Grade  or 
ratio  of 
expansion 

Hyperbolic 
logarithm 

Mean  pres- 
sure of  steam 
during  the 
whole  stroke 

Percentage 
of   gain  in 
fuel  or  power 

I 

9 

X 

P 

% 

yV,  or  0.1 

10.0 

2.302 

3.302 

230.0 

-J  ,  or  0.125 

8.0 

2.079 

3.079 

208.0 

J-,  or  0.166 

6.0 

1.791 

2.791 

179.0 

ft,  or  0.2 

5.0 

1.609 

2.609 

161.0 

1  ,  or  0.25 

4.0 

1.386 

2.386 

139.0 

ft,  or  0.3 

3.33 

1.203 

2.203 

120.0 

i  ,  or  0.333 

3.0 

1.099 

2.099 

110.0 

|  ,  or  0.375 

2.66 

0.978 

1.978 

97.8 

fV  or  0.4 

2.5 

0.916 

1.916 

91.6 

|,  or  0.5 

2.0 

0.693 

1.693 

69.3 

ft-,  or  0.6 

1.666 

0.507 

1.507 

50.7 

f  ,  or  0.625 

1.6 

0.47 

1.47 

47.0 

|,  or  0.666 

1.5 

0.405 

1.405 

40.5 

ft,  or  0.7 

1.42 

0.351 

1.351 

35.1 

f,  or  0.75 

1.33 

0.285 

1.285 

22.3 

-ft,  or  0.8 

1.25 

0.223 

1.223 

20.5 

A,  or  0.875 

1.143 

0.131 

1.131 

13.1 

,  or  0.9 

1.11 

0.104 

1.104 

10.4 

TABLE  No.  2. 

It  must  be  understood  that  the  Mean  Pressure  as  estimated 
in  the  preceeding  examples,  is  the  absolute  pressure,  measured 
from  the  line  of  perfect  vacuum. 

In  non-condensing  engines  under  good  conditions,  the 
average  back  pressure  will  be  from  one  to  two  pounds  above 


A  nd  Its  Appliances.  133 

the  atmosphere,  or  about  16  pounds  absolute;  and  which  must 
be  deducted  from  the  results  obtained.  The  remainder  will  be 
the  average,  or  Mean  Effective  Pressure. 

In  condensing  engines  the  back  pressure  will  average  from 
about  4^  to  5  pounds  irrespective  of  the  atmosphere,  being  a 
loss  through  imperfect  vacuum ;  and  which  must  also  be  de- 
ducted in  this  case,  in  order  to  obtain  the  Mean  Effective  ^Pres- 
sure. In  either  case  the  exact  amount  of  back  pressure  to  be 
deducted  will  vary ;  and  such  variation  will  depend  mostly  up- 
on circumstances,  and  local  conditions. 

The  theoretical  economy  of  using  steam  expansively  is 
given  in  Table  No  2,  which  contains  the  hyperbolic  logarithm 
for  numbers  running  from  10,  the  grade,  or  ratio  of  expansion, 
representing  o.  i,  or  i-io  cut-off,  to  i.n,  representing  0.9,  or 
9-10  cut-off,  and  which  may  be  considered  of  sufficient  range 
for  application  to  the  expansion  of  steam  in  engines  for  all 
practical  purposes. 

The  first  column  L  represents  the  portion  of  stroke  at 
which  steam  is  cut-off,  the  second  G  the  grade,  or  ratio  of  ex- 
pansion, the  third  X  the  hyperbolic  logarithm  of  the  number 
or  grade  of  expansion ;  the  fourth,  the  mean  pressure  of  steam 
during  the  whole  stroke,  and  the  fifth  column  the  percentage 
of  gain  in  power. 

The  per  cent  of  gain  by  expansion  is  obtained  by  multiply- 
ing the  logarithm  of  the  number  of  expansions  by  100. 

In  the  Table  no  deductions  are  made  for  a  reduction  of 
the  temperature  of  the  steam  during  expansion,  nor  for  any 
loss  through  back  pressure. 

In  expansion,  the  same  relative  advantages  occur,  as 
given  in  the  table  whatever  may  be  the  initial  pressure  of  the 
steam. 

The  results,  in  reference  to  the  percentage  of  gain  as  shown 
by  the  table,  is  as  before  stated,  theoretical,  as  from  the 


134 


Steam  Engine  Indicator 


resistance  to  expansion  of  the  back  pressure  in  a  cylinder,  and 
from  the  loss  of  temperature  of  the  steam  by  cooling,  and  also 
from  the  friction  of  the  steam  passages,  these  results  in  practice 
are  very  materially  reduced. 

The  pressure  of  the  atmosphere  is  always  included  in  cal- 
culating the  expansion ;  therefore  must  be  deducted  from  the 
results  in  all  non-condensing  engines. 

CONSTANTS    FOR   FINDING   THE    AVERAGE    PRESSURE    IN    THE 
CYLINDER   WITH   ANY    PRESSURE    OF    STEAM. 


Percentage 
of  the 
stroke  at 
which 
steam  is 
cut  off. 

Constant. 

Percentage 
of  the 
stroke  at 
which 
steam  is 
cut  off. 

Constant. 

Percentage 
of  the 
stroke  at 
which 
steam  is 
cut  off. 

Constant. 

Percentage 
of  the 
stroke  at 
which 
steam  is 
cut  off. 

Constant. 

l°/o 

•0560 

21% 

5377 

41°/0 

•7758 

61°/0 

•9114 

2 

•0982 

22 

•5529 

42 

•7841 

62 

•9162 

3 

•1321 

23 

•5679 

43 

•7920 

63 

•9200 

4 

•1688 

24 

5823 

44 

•8010 

64 

•9264 

5 

•1998 

25 

•5967 

45 

•8088 

65 

•9298 

6 

•2288 

26 

•6102 

46 

•8164 

66 

•9340 

7 

2563 

27 

•6237 

47 

•8235 

67 

•9385 

8 

.•2821 

28 

•6365 

48 

•8318 

68 

•9427 

9 

•3067 

29 

•6484 

49 

•8396 

69 

•9461 

10 

•3302 

30 

•6612 

50 

•8466 

70 

•9496 

11 

•3527 

31 

•6726 

51 

•8536 

71 

•9531 

12 

•3743 

32 

•6842 

52 

•8592 

72 

•9588 

13 

•3952 

33 

•6958 

53 

•8660 

73 

•9595 

14 

•4152 

34 

•7066 

54 

•8722 

74 

•9620 

15 

•4345 

35 

•7172 

55 

•8779 

75 

•9638 

16 

•4532 

36 

7276 

56 

•8846 

80 

-9784 

17 

•4712 

37 

•7378 

57 

•8904 

85      . 

•9878 

18 

•4885 

38 

•7477 

58 

•8962 

90 

•9945 

19 

•5055 

39 

•7567 

59 

•9002 

95 

•9960 

20 

•5219 

40 

•7665 

60 

•9062 

100 

1-0000 

TABLE  No.  3. 

In  condensing  engines  a  deduction  must  be  made  for  im- 
perfect vacuum ;  usually  amounting  to,  from  2^  to  3  pounds 
per  square  inch. 

The  Table  No.  3  contains  constants  for  finding  the  average 
pressure  in  the  cylinder,  f oY  any  percentage  of  the  stroke  (from 


And  Its  Appliances. 


135 


i  to  100)  at  which  the  steam  is  cut-off,  and  on  account  of  its 
simplicity,  will  be  found  in  many  cases  more  convenient  in 
finding  the  average  pressure  on  the  piston  throughout  the 
stroke  (from  a  given  initial),  than  by  the  ordinary  method  of 
using  hyperbolic  logarithm. 

The  rule  by  which  to  use  the  constants  is  as  follows : 
Multiply  the  constant  opposite  the  known  per  cent  of  cut-off, 
by  the  total  pressure  of  the  steam  entering  the  cylinder ;  the 
product  will  be  the  total  average  pressure  on  the  piston. 

AVERAGE    PRESSURE    OF   STEAM    IN   THE   CYLINDEP    WITH    VAR- 
IOUS  INITIAL   PRESSURES   AND    DIFFERENT   RATES 
OF    EXPANSION. 


Initial 
pressure 
above 
atmos- 
phere in 
Ibs.'per 
sq.  inch. 

Percentage  of  the  stroke  at  which  steam  is  cut  off. 

10 

15      |      20             25 

30 

35 

40 

45 

50      |     60 

Average  pressure  >n  Ibs.  per  square  inch  during  the  whole  stroke. 

40 

18^1 

23-8 

28-6 

32-8 

36-6 

39-3 

421 

444 

46-5 

49-9 

45 

.  19-8 

262 

31-0 

35-8 

39-2 

430 

46-0 

48-6 

507 

54-4 

50 

21-5 

28-3 

338 

38-7 

43-0 

465 

49-9 

52-6 

55-0 

59-0 

55 

23-2 

30-5 

36-4 

417 

46-2 

50-2 

53-5 

56-7 

59-1 

63-3 

60 

24-7 

32-6 

39-0 

44-8 

495 

53-7 

57-4 

60-8 

63-4 

68-0 

65 

26-4 

34-8 

417 

47-7 

52-9 

573 

61-1 

64-8 

67-5 

725 

70 

28-0 

37-0 

44-1 

50-6 

56-1 

60-9 

65-0 

68-8 

71-8 

77-0 

75 

297 

39-2 

46-9 

53-7 

59-4 

64-3 

68-8 

72-9 

76-0 

81-5 

80 

31-3 

41-4 

49-4 

56-6 

62-8 

68-0 

72-7 

76-9 

80-2 

86'0 

85 

33-0 

435 

52-0 

59-6 

66-0 

71-5 

76-5 

80-9 

84-4 

90-6 

90 

347 

45-7 

54-7 

627 

69-5 

75-0 

,80-3 

84-9 

88-7 

95;3 

95 

363 

47-9 

57-5 

6R-9 

73-0 

78-6 

84  1 

89-0 

93-0 

100-0 

100 

38-0 

500 

59;9 

687 

76-0 

82-2 

88-0 

93-0 

973 

104-5 

110 

41-3 

54-5 

65-0 

74-6 

82-6 

89-3 

95-7 

101-0 

105-6 

113-0 

120 

447 

58-8 

70-1 

80-5 

89-3 

96-5 

103-3 

109-1 

114-0 

122-1 

130 

48-0 

63-1 

75-3 

86-5 

96-0 

103-8 

111-0 

117-2 

122-5 

131-3 

140 

51-2 

67-5 

807 

92-5 

102-6 

111-0 

118-6 

125:3 

131-0 

140-4 

150 

54-6 

71-9 

85-9 

98-5- 

109-3 

118-0 

1263 

133-4 

1395 

1495 

160- 

57-9 

76-2 

9M 

104-5 

116-0 

125-2 

134-0 

141-5 

148-0 

15S-5 

170 

61-2 

80-6 

96-3 

110-5 

122-6 

132-4 

141-8 

149-7 

1565 

167-5 

180 

64-5 

85-0 

101-5 

116-5 

129-3 

1397 

149-5 

1579 

165-0 

176T» 

190 

67-9 

893 

1067 

122-5 

136-0 

146-5 

157-3 

166-0 

173-5 

1857 

200 

71-1 

937 

112-0 

128-5 

142-6 

154-0 

165-0 

174-0 

182-0  1  194-8 

TABLE  No.  4. 

From   this   total,    subtract   the    average    back    pressure, 
(which  will  be  about  five  pounds  in  condensing  engines;  and  in 


136  Steam  Engine  Indicator 

non-condensing  engines  it  will  be  from  one  to  two  above  the 
atmosphere,  or  about  sixteen  pounds  total),  the  remainder 
will  in  either  case  be  the  average,  or  mean  effective  pressure. 

Table  No.  4  gives  the  average  pressure  of  steam  in  the 
cylinder  of  an  engine  for  the  various  initial  pressures,  above 
the  atmosphere  in  pounds  per  square  inch,  and  at  different 
rates  of  expansion. 

In  the  above  table,  no  allowance  is  made  for  back  pres- 
sure and  compression,  therefore  their  effect  must  be  subtracted 
from  the  above  average  pressures  in  order  to  ascertain  the 
mean  effective  pressure  on  the  piston. 

In  non-condensing  engines,  working  under  favorable  con- 
ditions, the  average  back  pressure  will  be  from  i.  to  2.  pounds 
above  the  atmosphere  or  ordinarily  a  total  of  about  16  pounds 
per  square  inch ;  this  amount  varies  according  to  location,  or 
elevation  above  the  sea  level. 

In  condensing  engines  the  back  pressure  will  average 
about  5  pounds,  irrespective  of  atmospheric  pressure. 


And  Its  Appliances.  137 


CHAPTER  XIX. 


THEORY   OF  ACTION   OF   STEAM    EXPANSION   IN   CYLINDERS. 


There  are  three  conditions  of  the  steam  cylinder,  withia 
which  the  action  of  the  steam  is  differently  influenced ,  as  follows : 

i st.  The  outer  surface  may  be  bare  or  unprotected  by 
any  covering  whatever  and  wholly  exposed  to  the  surrounding- 
medium. 

2d.  It  may  be  covered  by  some  non-conducting  material, 
such  as  felt  or  asbestos,  and  this  in  turn  protected  by  a  cover- 
ing of  wood  or  iron  on  the  outside. 

3d.  It  may  be  so  constructed  than  an  annular  chamber 
may  be  formed  on  the  outside,  to  be  filled  with  steam  from  the 
steam  chest,  steam  pipe,  or  from  any  convenient  place  where 
the  steam  is,  of  at  least,  the  same  temperature  as  the  entering 
steam  driving  the  piston. 

In  some  cases  the  cylinder  heads  are  also  cast  with  a 
chamber  for  containing  steam ;  this  is  called  steam  jacketing, 
and  the  jacket  itself  is  also  covered  with  a  non-conducting 
material. 

Therefore  an  explanation  of  the  generally  accepted  theory 
of  cylinder  condensation  may  be  of  assistance  to  many,  and  lead 
to  a  better  understanding  of  the  action  of  steam  within  the 
cylinder  of  an  engine  while  in  operation,  and  also  explain  the 
cause  of  such  condensation ;  which  invariably  occurs,  more  or 
less,  in  all  steam  engine  cylinders, 


138  Steam  Engine   Indicator 

The  action  of  steam  in  an  unjacketed  or  exposed  non-con- 
densing engine  cylinder  is  about  as  follows :  As  the  entering 
steam  at  the  commencement  of  the  stroke,  is  of  a  much  higher 
temperature  than  the  metal  parts,  with  which  it  comes  in  con- 
tact ;  (that  is,  the  interior  surface  of  the  cylinder,  piston,  and 
cylinder  head;)  consequently  a  portion  of  this  steam  is  con- 
densed in  heating  up  these  parts,  to  the  temperature  of  the 
entering  steam. 

As  the  piston  moves  forward  uncovering  fresh  surfaces  of 
the  cylinder,  the  condensation  continues  until  after  the  admis- 
sion valve  closes,  or  until  cut-off  takes  place. 

This  condensation  is  deposited  in  form  of  moisture  upon 
the  interior  walls  of  the  cylinder,  also  the  piston  and  cylinder 
head;  but  does  not  become  apparent  on  the  steam  line  of  the 
diagram,  because  the  place  of  that  condensed,  is  supplied  from 
the  steam  chest,  during  the  admission  of  steam. 

After  cut-off  the  steam  then  commences  to  expand,  and 
both  pressure  and  temperature  begin  to  diminish  in  a  corres- 
pondingly degree  ;  and  unless  the  steam  is  cut-off  very  early  in 
the  stroke  but  little  further  condensation  takes  place  ;  (although 
fresh  surfaces  of  the  cylinder  that  are  cooler  than  the  steam, 
continued  to  be  uncovered  as  the  piston  advances)  for  the 
reason  that  as  soon  as  the  temperature  of  the  steam  commences 
to  fall,  through  expansion,  the  head,  piston,  and  walls  of  the 
cylinder,  (already  heated  to  the  temperature  of  the  initial 
steam,)  begins  to  impart  a  portion  of  their  heat  to  the  expand- 
ing steam,  and  thus  prevent  further  condensation  (to  any  great 
extent)  taking  place.  As  represented  at  A  in  diagram  Fig.  66. 
As  the  piston  continues  to  advance,  the  expansion  is  carried 
still  further  and  in  consequence,  the  temperature,  as  well  as 
pressure,  is  correspondingly  lowered. 

During  this  time  the  higher  temperature  existing  in  the 
cylinder  walls,  piston  and  head,  has  been  gradually  imparted 
to  the  steam  condensed  in  the  early  part  of  the  stroke,  causing 


And  Its  Appliances.  139 

a  re-evaporation  of  this  moisture  and  thereby  raising  the  ter- 
minal pressure  in  the  cylinder.  Also  shown  in  Diagram  66 
at  B. 

When  the  piston  arrives  at  or  near  the  end  of  the  stroke, 
the  exhaust  valve  opens,  and  both  pressure  and  temperature  of 
the  steam  immediately  falls  to  an  extent  corresponding  to  the 
pressure  and  temperature  of  steam  at  atmospheric  or  back 
pressure. 

As  the  metal  has  still  a  higher  temperature  than  the  ex- 
haust, any  remaining  water  is  therefore  re-evaporated  during 


FIG.  66. 

the  return  stroke,  by  absorbing  heat  from  the  cylinder  walls, 
piston,  and  head,  thereby  still  further  reducing  their  tem- 
perature ;  and  this  extraction  of  heat  has  to  be  restored  to 
these  parts  again  at  the  expense  of  the  entering  steam  for  the 
next  forward  stroke  of  the  engine. 

In  a  very  early  cut-off  in  unjacketed  cylinders  the  steam 
suffers  further  condensation  for  some  distance  after  the  admis- 
sion valve  closes,  owing  to  the  cooler  portions  of  the  cylinder 
surface  which  are  being  exposed  (by  the  advance  of  the  piston,) 
liaving  to  be  heated  by  the  comparatively  small  volume  of  steam 
confined  within  the  cylinder  after  cut-off,  and  the  consequence 


140 


Steam  Engine   Indicator 


is  that  the  pressure  falls  for  some  distance  in  a  much  greater 
ratio,  than  that  due  to  expansion  alone.  As  the  piston  ad- 
vances however,  and  the  expansion  continues,  the  pressure 
falls,  and  consequently  the  temperature  of  the  steam  becomes  less 
than  that  of  the  interior  surface  of  the  cylinder,  and  other 
parts ;  thereby  causing  a  re-evaporation  of  the  moisture  which 
has  been  deposited  upon  their  surface  during  the  earlier  part 
of  the  stroke.  The  volume  of  steam  present,  being  thus  in- 


-T 


FIG  67. 

creased  by  this  re-evaporation,  the  pressure  also  becomes 
higher,  resulting  in  a  rise  of  the  expansion  line  during  the 
latter  part  of  the  stroke. 

Therefore  the  effect  of  this  action  on  the  expansion  curve 
of  an  actual  diagram,  with  an  early  cut-off,  is  to  cause  it  at  first 
to  fall  considerably  below,  (just  after  cut-off)  and  subsequently  to 
rise  above  the  true  theoretical  curve  toward  the  end  of  the  stroke. 

The  expansion  line  of  PMg.  67,  represents  the  partial  in- 
creased effects  of  cylinder  condensation, that  is  due  to  an  early 
cut-off,  showing  the  falling  below  at  a  point  A,  and  rise  above 
at  B,  of  the  actual  from  the  theoretical  curve  drawn  in  dotted 
line  from  the  point  of  cut-off  C. 


And  Its  Appliances.  141 

The  theoretical  curve  D,  B,  is  drawn  in  dotted  line  from 
the  point  B,  at  which  the  exhaust  valve  opens,  and  represents 
the  additional  work  that  might  be  done  by  steam  of  a  terminal 
pressure  T,  provided  condensation  were  prevented. 

This  deviation  from  the  true  curve  is  greatly  increased  by 
water  held  in  suspension  or  entrained  in  the  steam. 

It  is  therefore  important  that  the  initial  steam  be  prac- 
tically free  from  moisture. 

The  mutation  of  heat  back  and  forth,  (which  occurs  at 
every  stroke)  between  the  steam,  and  the  interior  surface  of 
the  cylinder  as  well  as  the  cylinder  head  and  piston,  take  place 
very  quickly,  and  effects  the  metal  of  these  parts  to  a  slight 
depth  only ;  as  there  is  not  sufficient  time  for  it  to  penetrate 
very  deeply,  especially  in  high  speed  engines. 

Steam  Jacketed  Cylinders.  The  action  which  takes  place 
in  a  steam  jacketed  cylinder  of  a  condensing  engine  is  some 
what  different ;  as  the  following  description  will  indicate : 

In  such  cases  the  jacket  is  arranged  to  be  supplied  con- 
stantly with  direct  steam  (either  through  the  steam  chest,  or 
steam  pipe)  of  the  same  temperature  and  pressure  as  the  initial 
steam  entering  the  cylinder ;  consequently  the  alternate  heat- 
ing, and  cooling  of  the  metal  that  occurs  in  an  unjacketed  cyl- 
inder, will  in  a  great  measure  in  this  case  be  prevented ; 
hence,  comparatively  no  initial  condensation  takes  place,  and 
the  steam  will  enter  the  cylinder  without  apparent  loss. 

The  piston  itself  being  partially  under  the  same  conditions 
as  before,  will  tend  continuously  to  condense  a  very  small  por- 
tion of  the  steam;  but  this  condensation,  (in  the  act  of  form- 
ing) will  at  once  be  re-evaporated ;  therefore  no  actual  conden- 
sation takes  place  during  expansion,  as  the  quantity  of  heat 
that  disappears  in  doing  work  is  steadily  supplied  by  the 
cylinder  walls. 


142  Steam  Engine    Indicator 

The  walls  in  turn  absorb  heat  from  the  steam  in  the  jacket, 
thereby  condensing  a  portion  of  the  steam,  but  the  jacket 
being  constantly  supplied  with  direct  steam,  maintains  the 
cylinder  at  nearly  a  uniform  temperature. 

When  the  exhaust  valve  opens,  and  communication  is- 
made  with  the  condenser,  (there  being  no  water  or  moisture  to- 
re-evaporate,) a  further  expansion  of  the  steam  occurs ;  there- 
<by  lowering  both  pressure  and  temperature. 

This  exhaust  steam  being  comparatively  dry,  receives  and 
parts  with  heat  slowly,-  and  therefore  does  not  absorb  as  much 
heat  from  the  cylinder  walls  when  expanding  into  the  con- 
denser, as  the  wet  steam  from  an  unjacketed  non-condensing 
cylinder ;  as  in  the  former  case. 

Although  the  steam  jacket  supplies  the  heat  necessary  to 
prevent  condensation,  and  also  to  heat  up  the  cylinder,  from  a, 
temperature  corresponding  to  the  exhaust,  to  that  of  the  initial 
or  entering  steam ;  yet  this  quantity  of  heat  is  much  less  than 
that  which  is  extracted  by  wet  steam  from  the  walls  of 
cylinders  that  are  unjacketed,  consequently  the  actual  gain 
effected  by  the  use  of  a  steam  jacket  on  a  cylinder,  is,  the 
difference  of  saving,  between  the  prevention  of  condensation 
in  the  cylinder  during  the  first  part  of  the  stroke,  and  the  loss, 
that  occurs  in  heating  the  exhaust  steam  during  the  return 
stroke ;  and  this  gain  may  in  many  cases  be  very  slight,  as  the 
saving  depends  principally  upon  the  fact  that  steam  absorbs 
heat  much  slower  than  water. 

t  In  preventing  this  condensation  in  the  cylinder,  the  heat 
abstracted  from  the  steam  jacket,  transfers  all  liquefaction  or 
condensation  of  the  steam  to  the  jacket ;  and  on  this  account 
some  engineers  at  the  present  time,  questions  its  utility  in  the 
matter  of  economy,  (also  considering  first-cost)  and  claim  that, 
the  condensation,  and  waste  of  steam  in  the  jacket,  is  more- 
than  that  lost  or  wasted  in  unjacketed  cylinders ;  the  excess 


And  Its  Appliances. 


being  due  to  increased  condensing,  and  radiating  surface  of 
the  jacket,  above  that  of  the  steam  cylinder. 

The  diagram  represented  in  Fig.  68  is  from  a  steam  jack- 
eted cylinder  and  it  will  be  seen  that  the  actual  curve  agrees 
very  closely  to  the  Isothermal. 

In  reference  to  the  efficiency  of  the  jacket  however,  all  re- 
sults depend  in  a  great  measure  upon  its  proper  construction, 
and  appliances;  and  also  in  providing  means  for  the  removal 
of  all  air  and  water  arising  from  condensation ;  and  utilizing 


FIG.  68. 

such   water,    as   fast   as  formed  by  returning  it  to  the  boiler ; 
thereby  preventing  the  accumulation  of  either  in  the  jacket. 

In  addition  to  this  and  to  insure  the  best  efficiency  it  is 
absolutely  essential  that  the  jacket  be  constantly  supplied  with 
dry  steam  of  a  temperature  fully  as  high,  in  all  cases,  as  that 
of  the  initial  steam  entering  the  steam  cylinder;  and  more  es- 
pecially in  engines  with  early  cut-off,  and  consequently  high 
expansion. 

Where  the  details  referred  to,  are  strictly  observed  and 
carried  out,  the  result  must  evidently  tend  more  or  less  to- 


144  Steam  Engine   Indicator 

better  economy  and  efficiency  in  engines,  by  the  use  of  the 
steam  jacket. 

On  the  contrary,  if  wet  steam,  or  steam  containing  a  large 
proportion  of  moisture  be  introduced  into  a  steam  jacketed  en- 
gine cylinder  in  the  beginning  of  the  stroke,  a  result  will  fol- 
low, which  will  be  the  opposite  of  economy,  and  end  in  con- 
siderable loss,  this  loss  arising  from  the  large  quantity  of  heat 
abstracted  from  the  jacket  during  the  stroke,  for  the  evapora- 
tion of  this  water  or  moisture  that  has  entered  the  cylinder. 

Therefore  to  insure  that  the  economy  and  efficiency  which 
is  expected  from  the  use  of  the  steam  jacket  be  realized,  it  is 
very  essential  that  all  the  requirements  before  mentioned  for 
its  proper  performance,  should  be  assured,  otherwise  the  jacket 
may  be  quite  ineffectual ;  its  theoretical  efficiency  wholly 
destroyed,  and  its  utility  consequently  questioned. 

In  a  great  majority  of  cases  at  the  present  time,  cylinder 
jacketing  is  accomplished  in  accordance  with  the  second  con- 
dition mentioned ;  viz,  that  of  thoroughly  covering  the  whole 
of  the  exterior  surface  of  the  cylinder,  and  steam  chest,  with 
some  non-conducting  material  as  felt,  wool,  or  asbestos,  and 
secured  thereto  by  an  extra  covering  of  wood  or  iron ;  com- 
pletely enveloping  the  whole. 

This  combination  of  covering  where  suitably  applied,  ap- 
pears to  give  general  satisfaction,  as  many  builders  of  our 
best  modern  engines  testify;  by  the  almost  exclusive  use  of 
some  suitable  material  for  cylinder  jacketing,  on  this  prin- 
ciple. 

Also  in  many  cases  where  engine  cylinders  are  covered 
and  protected  in  the  manner  just  described,  and  having  steam 
tight  valves,  and  piston,  it  is  frequently  found  that  the  expan- 
sion line  of  the  diagrams  therefrom,  agree  very  nearly  with 
the  isothermal  or  true  theoretical  curve  as  represented  in 
Fig.  69. 


And  Its  Appliances.  145 

Therefore  it  is  readily  seen  from  the  diagrams  Fig.  68  and 
Fig.  69  the  advantages  to  be  derived  by  either  of  the  latter 
conditions  or  methods  of  cylinder  jacketing,  to  secure  the 
greater  economy,  and  efficiency  in  the  engine ;  above  that  of 
one  from  an  exposed  or  unprotected  steam  cylinder  with  an 


FIG.  69. 

early  cut-off  as  represented  in  the  diagram  Fig.  67.  In  order  to 
obtain  Indicator  diagrams  that  shall  be  accurate  exponents, 
and  represent  the  true  action  of  steam  expansion  within  the 
cylinder,  it  is  absolutely  essential  that  the  valves,  and  piston 
of  the  engine  be  practically  steam  tight ;  and  also  that  the  In- 
dicator itself  have  perfect  and  unimpeded  freedom  of  move- 
ment in  all  its  parts,  when  under  pressure  and  temperature  of 
the  steam  present.  The  exact  measure  of  the  tension,  or  in 
other  words,  the  strength  of  the  spring  used,  is  also  of  great 
importance ;  as  the  accuracy  of  all  computations  based  upon 
the  form  of  the  diagram,  for  obtaining  the  Mean  Effective 
Pressure,  acting  against  the  piston  depends  upon  the  correct- 
ness of  the  spring;  therefore  its  accuracy  should  be  determined 
and  established,  (by  comparison  with  a  correct  steam  guage), 
before  any  elaborate  tests  are  anticipated.  This  may  be  ac- 
complished in  a  satisfactory  manner  by  means  of  the  simple 
Indicator  spring  testing  device  represented  and  described  in  Fig. 
84,  Chapter  XXII. 


146  Steam  Engine  Indicator 


CHAPTER  XX. 


READING    THE    DIAGRAM. 


The  principal  and  most  positive  information  to  be  derived 
from  the  reading  of  an  actual  indicator  diagram,  is,  the  meas- 
ure of  the  force  or  pressure  in  the  cylinder,  acting  upon  the 
opposite  sides  of  the  piston,  at  any  and  all  points,  during 
one  complete  revolution  of  the  engine ;  hence  the  actual  card,, 
as  compared  with  the  theoretical  diagram,  (under  similar  con- 
ditions) indicates  the  efficiency  and  economy  of  the  engine ; 
and  all  other  information  must  also  be  acquired  through  ex- 
ceedingly careful  consideration,  and  reasoning  in  the  study  of 
the  diagrams ;  and  conclusions  arrived  at,  therefrom  in  accord- 
ance with  an  exercise  of  the  best  judgment  of  the  engineer. 

The  figures  traced  by  the  pencil  will  vary  in  outline  in 
different  engines,  and  also  from  the  same  engine  under  vary- 
ing conditions,  due  to  a  number  of  causes ;  as  leakage  of  valves, 
condensation  and  re-evaporation  of  the  condensed  steam  in 
the  cylinder,  construction,  and  the  adjustment  of  valves,  condi- 
tion of  the  steam,  etc. 

These  effects  will  be  more  apparent  along  the  expansion 
curve  especially ;  and  as  a  consequence  the  actual  curve  will 
very  rarely  coincide  exactly  with  the  true  theoretical  curve. 

Therefore  it  is  very  essential  that  all  cards  traced  by  the 
indicator  should  accurately  represent  the  duty  performed  by 
the  engine ;  as  the  accuracy  of  all  such  investigations  depends 
entirely  upon  the  correctness  of  the  diagrams. 


And  Its  Appliances.  147 

Upon  an  examination  of  the  steam  expansion  curve  of  in- 
dicator diagrams  it  will  be  found  (almost  invariably),  that  the 
Terminal  pressure  is  relatively  too  high  (from  a  given  cut-off), 
as  compared  with  the  true  theoretical  curve ;  the  amount  in- 
creasing as  the  ratio  of  expansion  increases:  as  shown  in 
Fig.  66 
B 


FIG.  70. 

This  result  may  be  due  to  either  of  two  causes,  or  to  both 
combined. 

i  st.  To  leaky  steam  or  admission  valves,  through  which 
the  steam  is  enabled  to  pass  into  the  cylinder,  after  the  closure 
of  such  valve ;  or  in  other  words,  after  the  point  at  which  cut- 
off is  supposed  to  have  taken  place ;  arid  thereby  producing  a 
higher  terminal,  than  would  otherwise  appear  with  steam  tight 
valves. 

2nd.  To  a  re-evaporation  of  the  entering  steam  that  is 
condensed  in  the  earlier  part  of  the  stroke,  through  coming  in 
contact  with  the  interior  walls  of  the  cylinder,  which  have  been 
cooled  to  a  temperature  corresponding  to  the  lower  pressure  of 
the  escaping  steam,  during  its  exhaust. 


148  Steam  Engine  Indicator 

In  some  cases  however  the  expansion  curve  of  the  actual 
diagram  will  be  found  falling  below  the  true  or  theoretical 
curve  throughout  its  entire  length ;  as  shown  in  Fig.  70,  evi- 
dently due,  to  leaky  piston,  and  exhaust  valves;  this,  also  in 
connection  with  exposed  or  unjacketed  steam  cylinders. 

But  it  frequently  happens  that  cards  are  found  wherein 
the  expansion  curve  coincides  very  nearly  with  the  isothermal 
or  theoretical,  although  they  have  been  taken  from  engines  in 
which  both  valves  and  piston  are  known  to  leak  badly. 

In  such  cases  the  leakage  through  the  admission  valve 
after  closing  is  just  sufficient  to  restore  the  steam  lost  through 
a  leaky  piston,  and  the  result  under  such  circumstances,  are 
that  the  two  curves  will  be  a  very  near  approach  to  each  other. 

Such  cards  from  observation  alone  have  the  appearance  of 
good  efficiency  and  economy  in  the  engine ;  when  in  fact  the 
opposite  of  this  prevails,  and  an  extravagant  loss  and  waste  of 
steam  is  the  consequence ;  all  arising  from  a  leaky  condition  of 
these  parts. 

The  loss  of  steam  from  this  cause,  and  also  from  cylinder 
condensation  is  not  accounted  for  by  the  indicator,  hence  does 
not  appear  in  the  diagrams,  and  is  only  made  apparent  by  a 
comparison  of  the  water  consumption  per  horse  power  (as  com- 
puted from  the  diagram),  with  the  actual  amount  of  water  that 
has  been  supplied  to  the  boiler. 

An  important  matter  to  be  ascertained  in  reference  to  all 
indicators ;  is,  whether  the  vertical  or  admission  line  on  the 
diagram,  made  by  the  pencil  (when  in  contact  with  the  paper 
on  the  drum)  is  exactly  perpendicular  to  the  atmospheric,  or 
horizontal  line,  that  is  made  by  the  pencil,  when  in  contact 
with  the  drum  while  rotating. 

A  leaning  of  the  admission  line  either  forward  or  back, 
thereby  causing  it  to  be  out  of  square  with  horizontal  line, 
tends  to  be  misleading  in  reference  to  the  proper  adjustment 
of  the  valves,  especially  if  a  fault  of  this  kind  exists  in  the 


And  Its  Appliances. 


149 


instrument,  and  not  previously  known.  This  fact  may  easily  be 
determined  at  any  time  before  placing  the  spring  in  the  instru- 
ment, by  simply  placing  the  paper  upon  the  drum  the  same  as 


FIG.  71. 

for  taking  diagrams,  and  bring  the  pencil  in  contact  with  it ; 
then  cause  the  drum  to  rotate  once  back  and  forth  by  means 
of  the  cord  attached  to  the  indicator,  thereby  making  a  hori- 


FIG.  72. 

zontal  line  on  the  paper ;  then  mark  a  perpendicular  to  this  by 
raising  the  pencil  by  hand  to  its  extreme  height.     Remove  the 


Steam  Engine  Indicator 


paper  from  the  drum,  and  compare  its  correctness  with  any 
ordinary  square  or  right  angle  triangle  at  hand,  as  shown  in 
Fig.  71.  Any  inclination  or  leaning  of  the  admission  line  in 
indicator  diagrams,  either  forward  or  back,  as  in  Fig.  72  and 
Fig.  73,  is  usually  construed  and  considered  to  be  an  im- 
proper adjustment  of  the  valves. 

For  example.  In  reviewing  the  diagram  represented  in 
Fig.  72  ;  from  the  fact  of  a  leaning  forward  of  the  admission 
line,  the  time  of  opening  of  the  valve  for  steam  admission, 
would  ordinarily  be  assumed  to  be  too  late,  or  indicating  in- 
sufficient lead ;  and  in  consequence  the  piston  has  advanced  a 
portion  of  the  stroke,  (as  shown  at  A),  before  the  initial  pres- 
sure has  reached  its  highest  point ;  resulting  to  a  certain  de- 
gree, in  a  loss  of  power,  and  efficiency  in  the  engine. 

Again  suppose  in  a  diagram  the  results  are  as  represented 
in  Fig.  73,  where  the  admission  line  inclines  outward;  this 


FIG.  73. 

might  indicate  either  a  too  early  opening  of  the  steam  valve, 
thereby  admitting  steam  in  the  cylinder  before  the  piston  had 
completed  the  stroke ;  or  a  too  early  closing  of  the  exhaust  at 
that  end  of  the  cylinder,  thus  causing  excessive  compression ; 
either  of  which  would  also  cause  a  loss  of  efficiency  and  power. 


A  nd  Its  Appliances. 

Most  types  of  indicators  after  their  being  in  use  for  a 
length  of  time,  are  liable  to  certain  defects,  or  disarrangement 
more  or  less  in  their  pencil  movement ;  (and  these  defects  some- 
times appears  in  new  instruments)  and  which  prevents  the  ini- 
tial pressure  or  vertical  line  as  traced  upon  the  paper,  from  be- 
ing at  a  right  angle  or  perpendicular  to  the  atmospheric  line ; 
and  in  such  case  the  instrument  is  usually  designated  as  out  of 
square. 

As  a  consequence,  the  admission  line  at  either  end  of  the 
diagram,  will  be  inclined  to  the  perpendicular,  as  appears  by 


FIG.  74. 

the  dotted  lines  A,  A,  in  the  diagrams  Fig.  74,  and  which  may 
be  wholly  due  to  such  incorrectness  in  the  indicator  as  stated ; 
notwithstanding  the  valve  adjustment  of  the  engine  may  be 
practically  all  that  can  be  desired. 

This  discrepancy  very  often  arises  from  careless  handling, 
and  from  culpable  neglect,  and  abuse  of  the  instrument  in  var- 
ious ways.  Where  a  defect  of  this  description  exists  in  the  in- 
strument, it  is  generally  advisable  to  send  it  at  once  to  the 
maker,  to  insure  that  the  necessary  correction  be  properly  and 
satisfactorily  accomplished. 


152  Steam  Engine  Indicator 


CHAPTER  XXL 


DIFFERENT   METHODS    OF   COMPUTING   THE   AMOUNT   OF   STEAM 
ACCOUNTED    FOR   BY    THE   INDICATOR. 


If  the  number  of  cubic  feet  occupied  by  the  steam  in  an 
engine  cylinder,  and  the  pressure  it  exerts  against  the  piston 
at  any  point  of  the  stroke  be  known,  the  number  of  pounds 
which  the  steam  weighs  may  be  computed. 

The  weight  of  the  steam  at  any  point,  less  the  weight  re- 
maining in  the  cylinder  at  compression,  is  the  weight  account- 
ed for  by  the  indicator. 

The  weight  accounted  for  on  one  stroke,  multiplied  by 
the  number  of  strokes  per  hour,  and  divided  by  the  indicated 
horse  power,  is  the  amount  of  steam  accounted  for,  per  indi- 
cated horse  power  per  hour. 

This  computation  requires  a  knowledge  of  the  volume  of 
the  clearance  space  in  the  cylinder;  that  is,  the  cylindrical 
space  between  the  cylinder  head  and  the  piston,  when  the  pis- 
ton is  at  the  end  of  its  stroke,  and  also  includes  the  volume  of 
the  steam  ports  and  passages  which  conducts  the  steam  from 
the  admission  valve  to  the  cylinder,  and  also  from  the  cylinder 
to  the  exhaust  valve. 

The  water  consumption  of  an  engine  (as  stated  in  another 
chapter)  is  the  measure  of  its  economy,  but  the  exact  amount 
is  not  determinable  from  the  diagram,  because  that  gives  the 
pressure  of  steam  only. 


And  Its  Appliances. 


153 


Of  the  water  that  has  been  carried  over  with  the  steam,  or 
of  the  steam  that  has  been  condensed  by  coming1  in  contact 
with  the  comparatively  cold  surfaces  of  the  cylinder,  the  dia- 
gram gives  110  record. 

We  know  however,  that  at  least,  the  amount  of  steam  ac- 
counted for  by  the  indicator  has  passed  through  the  cylinder ; 
and  in  fact,  we  know  that  sometimes  a  much  larger  amount 
has  been  used. 

One  method  of  ascertaining  the  amount  accounted  for  by 
an  indicator  is  to  calculate  the  piston  displacement,  plus  the 
clearance  space  for  a  given  time,  in  cubic  feet,  up  to  a  certain 
point  in  the  stroke  before  the  exhaust  opens,  and  multiply  this 
volume  by  the  weight  of  a  cubic  foot  of  steam  of  the  absolute 
pressure  at  this  point. 


FIG.  75. 

This  method  is  described  in  the  diagram  Fig.  75  and  is  as 
follows :  Draw  the  vacuum  line  V.  V. ,  and  the  clearance  line 
D.  and  select  some  point  on  the  expansion  curve,  as  at  C- 
where  it  is  known  that  both  the  steam  and  exhaust  valve  are 
closed  and  wherever  it  is  possible,  have  this  point  C.  at  a 


154  Steam  Engine  Indicator 

distance  from  the  end  of  the  diagram  equal  to  the  clearance  dis- 
tance D. 

Where  this  can  be  done,  then  the  volume  to  point'C.,  in- 
cluding clearance,  will  just  equal  the  piston  displacement 
which  is  the  area  of  the  piston  multiplied  by  the  length  of 
stroke. 

Where  this  cannot  be  done,  then  find  volume  to  point  C, 
including  clearance,  which  if  multiplied  by  the  weight  of  a 
cubic  foot  of  steam  of  the  absolute  pressure  at  the  point  se- 
lected will  give  the  weight  of  the  steam  contained  in  the  cylin- 
der at  such  point. 

The  volume  at  point  C  may  be  found  as  follows : 

Assume  the  cylinder  of  an  engine  to  be  12  inches  in  diam- 
eter, (113.09  square  inches  in  area)  with  a  stroke  of  piston  of 
30  inches  running  90  revolutions  per  minute ;  the  area  of  pis- 
ton rod  being  6.18  inches;  the  clearance  being  five  per  cent, 
and  the  scale  of  the  spring  40. 

From  the  area  of  the  cylinder,  deduct  one-half  the  area  of 
the  piston  rod  (6. 18^-2  =  3.09  inches)  hence  ;  1 13.09—3.09=  1 10 
square  inches  as  the  mean  area  of  the  piston. 

The  total  piston  displacement  per  stroke  therefore  will  be, 
the  mean  area  of  piston  in  inches  multiplied  by  length  of 
stroke,  also  in  inches,  110X30=3300  cubic  inches  per  single 
stroke  of  the  engine. 

The  displacement  to  the  selected  point  C,  may  then  be 
ascertained,  by  multiplying  the  total  displacement,  (3300  cubic 
inches)  by  the  distance  that  point  C,  is  from  the  initial  end  of 
the  diagram,  or  from  line  E,  and  dividing  this  product  by  the 
total  length  of  the  diagram,  or  line  A,  B,  for  example:  The 
length  of  the  line  C,  E,  is  3.56  inches,  and  the  length  of  A,  B, 


is  3.75  inches,  therefore      ———-  =  3132.8,  cubic  inches. 

To  this  must  be  added  five   per  cent,  for  clearance,   or 
3300X  .05=  165.  then  3132.8+165  =  3297.8  cubic  inches  occupied 


A  nd  Its  Appliances  .  155 

by  steam  at  point  C.  The  engine  running  90  revolutions 
per  minute  consequently  makes  90  X  2  X  60  =  10800  single 
strokes  per  hour;  therefore-  the  displacement  per  hour  is 

3297.  8x  10800  ,  .     . 

~-*£  —  _  -  =20611  cubic  feet. 
1728 

Now  with  the  scale  of  the  spring,  (40)  with  which  the  dia- 
gram was  taken,  measure  the  absolute  pressure  from  the  va- 
cuum line  to  point  C,  and  opposite  this  pressure  in  the  Table 
No.  8  of  properties  of  saturated  steam  will  be  found  the  weight 
of  a  cubic  foot  of  steam  at  that  pressure. 

The  absolute  pressure  at  point  C,  is  26  pounds  and  the 
weight  of  a  cubic  foot  of  steam  at  this  pressure  is  .065,  hence 
the  weight  of  steam  at  this  point  per  hour  is  2o6nX.o65  =  - 
1339.71  pounds. 

From  this  amount  however  the  steam  saved  by  compression 
caused  by  the  closing  of  the  exhaust  valve  before  the  end  of 
the  stroke,  must  be  deducted  ;  the  remainder  being  the  actual 
consumption  of  steam  as  accounted  for  by  the  indicator, 

The  process  by  which  to  ascertain  the  amount  of  this  de- 
duction is  as  follows  : 

From  the  selected  point  C,  draw  a  line  parallel  with  the 
vacuum  line  to  E,  intersecting  the  compression  curve  at  point 
F.  ;  multiply  the  accounted  consumption  by  the  distance  from 
C  to  F,  and  divide  this  by  the  distance  from  C.  to  E. 

The  length  of  the  line  from  C.  to  F.  is  3.32  inches,  and 
that  of  the  line  from  C.  to  E.  is  3.56  inches,  hence 

339-7       3«3   —!  249,  39  pounds  of  steam  exhausted  per  hour, 

corrected  for  both  clearance  and  compression.  The  Mean 
Effective  Pressure  of  the  above  diagram  (measured  by  Plani- 

meter)  being  37.5  pounds  per  square  inch,  the  Horse  Power  is 

• 

-  ^—5  —  ^-=56.25,    hence   the    steam   accounted   for  per 
33000 


horse  power  per  hour  will  be  —  —  22.21  pounds. 


156  Steam  Engine  Indicator 

A  somewhat  simpler  method  of  determining-  the  same  re- 
sult, is  to  continue  the  expansion  curve  of  the  diagram  in  its 
gradual  descent,  to  the  end  of  the  stroke,  and  by  that  means 
locate  the  terminal  pressure  as  at  T,  Fig.  76. 


FIG.  76. 

This  point  may  be  found  according  to  the  method  des- 
cribed for  constructing  the  theoretical  curve  as  explained  in 
Fig,  56  Chapter  XIV,  or  may  be  traced  by  hand  from  the  point 
of  exhaust  opening  on  the  expansion  curve,  to  the  completion 
of  the  stroke ;  and  which  will  be  sufficiently  near  in  cases 
where  no  great  accuracy  is  desired. 

The  process  by  calculation  is  to  find  the  total  mean  dis- 
placement of  the  piston  for  the  whole  stroke,  plus  the  clearance 
in  cubic  feet  per  hour. 

Multiply  this  by  the  weight  of  a  cubic  foot  of  steam  at  the 
terminal  pressure  T,  and  divide  this  product  by  the  Indicated 
Horse  Power. 

The  quotient  is  the  number  of  pounds  of  steam  entering 
the  cylinder  per  horse  power  per  hour.  For  example  :  Assum- 
ing the  engine  data  to  be  the  same  as  in  the  preceeding; 


A  nd  Its  Appliances.  1 5  7 

example ;  therefore  the  mean  piston  displacement  per  single 
stroke  in  this  case  will  be  3465  cubic  inches;  which  if  multi- 
plied by  10806  the  number  of  single  strokes  per  hour,  and  di- 
vide by  (1728)  the  number  of  cubic  inches  in  a  cubic  foot,  the 
quotient  will  be  the  total  piston  displacement  in  cubic  feet  per 
hour,  that  is,  3465XiQ8oo=2i656 

I  728 

The  absolute  terminal  pressure  being  2  5  pounds  per  square 
inch,  the  weight  of  a  cubic  foot  of  steam  at  that  pressure,  ac- 
cording to  the  table  is  .063  pound;  therefore  2i656x.o63  = 
1364.32  pounds,  which  divided  by  the  indicated  horsepower 
of  the  diagram  (56.25)  is  equal  1353. 50-=- 56. 25  =  24. 25  the  num- 
ber of  pounds  of  steam  entering  the  cylinder  per  horse  power 
per  hour. 

And  this  would  also  be  the  actual  amount  of  steam  ex- 
hausted, were  it  not  for  the  fact  that  it  is  exhausted  above  va- 
cuum from  which  the  pressure  is  calculated ;  also  a  portion  of 
it  is  saved  in  the  clearance  space  upon  the  return  of  the  piston, 
and  this  saving  is  still  further  increased  by  the  closure  of  the 
exhaust  valve  before  the  end  of  the  stroke  ;  therefore  the  actual 
indicated  consumption  will  be  minus  this  amount. 

This  correction  may  be  made  as  follows : 

From  the  terminal  pressure  T,  draw  a  line  T  2,  parallel 
with  the  vacuum  line,  thereby  intersecting  the  compression 
curve  at  i,  at  which  point  the  quantity  of  steam  exhausted 
from  the  clearance  has  been  restored,  and  the  consumption  will 
be  as  much  less  than  the  rule  shows,  as  the  line  T.  i.  is  shorter 
than  the  line  T.  2.  or  the  length  of  the  diagram. 

Consequently  to  find  the  corrected  rate,  multiply  the  result 
as  found  by  the  rule  (24.25)  by  the  length  of  the  T.  1.^3.47 
inches,  and  divide  by  the  length  of  the  line  T.  2  =  3.75  inches, 

hence  -lllJJ — 5-^  =  2  2. 43  pounds  per  Indicated  Horse  Power 

*3  *  /  3 

per  hour ;  the  corrected  rate  for  both  clearance  and  compression. 


158  Steam  Engine  Indicator 

The  volume  of  the  cylinder,  and  the  number  of  strokes 
being-  factors  in  the  computation  of  the  amount  of  steam  ac- 
counted for  in  any  given  time,  and  the  same  also  being  factors 
in  the  calculation  of  power  developed,  consequently  for  this 
reason  it  is  not  necessary  to  take  these  quantities  into  consid- 
eration, when  only  the  amount  accounted  for  per  horse  power 
per  hour  is  desired. 

The  above  fact  provides  another,  and  much  more  simple 
method  of  computing  the  rate  of  water  consumption ;  in  which 
the  piston  displacement  is  not  required,  and  which  is  indepen- 
dent of  any  knowledge  of  the  size  or  speed  of  the  engine ;  the 
diagram  alone  being  sufficient ;  but  it  is  necessary  however  to 
know  the  mean  effective  pressure. 

This  rate  may  be  found  by  the  following  rule  :  Divide 
the  constant  number  859375  by  the  volume  of  steam  at  the  ter- 
minal pressure,  and  by  the  mean  effective  pressure. 

The  quotient  will  be  the  water  consumption  per  horse 
power  per  hour  uncorrected  for  compression  and  clearance. 

This  correction  is  made  in  the  same  manner  as  that  given 
in  the  previous  method. 

This  constant  859375  is  the  number  of  pounds  of  water 
that  would  be  used  in  one  hour  by  an  engine  developing  one 
horse  power,  if  run  by  water,  (instead  of  stean?)  at  one  pound 
pressure  per  square  inch. 

The  process  is  based  on  the  following  considerations :  A 
standard  horse  power  is  33000  pounds  raised  one  foot  per  min- 
ute, or  33000  foot  pounds,  which  is  33000x60—1,980,000  foot 
pounds  per  hour,  or  i,98o,ooox  12  =  23,760,000  inch  pounds 
per  hour.  The  latter  number  of  pounds  on  being  raised  one 
inch  per  hour,  requires  the  same  expenditure  of  energy,  as  to 
lift  33000  pounds  one  foot  per  minute;  each  being  the  equiva- 
lent of  the  other. 

Now  suppose  the  engine  to  be  run  by  water,  (instead  of 
steam)  at  one  pound  pressure  per  square  inch,  and  the  number 


A  nd  Its  Appliances. 


159 


of  cubic  inches  in  a  pound  of  distilled  water  being  27.648  then 
23, 760, ooo-i- 27, 648  =  859375  which  is  the  desired  constant, 
and  which  is  the  number  of  pounds  of  water  per  indicated 
horse  power  per  hour  that  would  be  consumed  by  an  engine 
driven  by  water,  (instead  of  steam)  at  one  pound  mean  effect- 
ive pressure. 

Example :     Assume  the  diagram  shown  in  Fig.  77,  to  be 
one  from  an  engine  of  12  inches,  diameter  of  cylinder,  and  24 


*| 

f\ 

\ 

\ 

\ 

\ 

V 

% 

\^^  __  '••••:/;  "•_ 

A 

\ 

2 

*^^_^ 

1 

^ 

Vi 

*-^ 

_U^i 

1 

A 

1    MX 

is- 


FIG.  ,77. 


inches  stroke  running  100  revolutions  per  minute,  the  scale  of 
the  spring  40. 

The  mean  effective  pressure  of  the  diagram  is  found  to  be 
42  pounds  per  square  inch,  when  measured  either  by  ordinates 
or  by  planimeter. 

The  absolute  terminal  pressure  T.  V,  is  28  pounds,  and 
the  volume  at  that  pressure  (as  given  in  table  No.  8)  is 
883,  that  is  one  cubic  inch  of  water  at  a  temperature  of  60  de- 
grees, makes  883  cubic  feet  of  steam  at  28  pounds  pressure  per 
square  inch. 


160  Steam  Engine  Indicator 

nee  by  the  rule  the  rate  of  water  c 

=  23.17  of  water  per  indicated  horse  power  per  hour. 


Hence  by  the  rule  the  rate  of  water  consumption  will  be 
859375 


883X42 

But  in  this  case  some  steam  is  saved  by  the  closure  of  the 
exhaust  valve  before  the  end  of  the  stroke,  while  some  is 
wasted  by  exhausting  from  the  clearance  at  a  pressure  greater 
than  the  back  pressure,  and  the  above  calculation  so  far  makes 
no  allowance  for  either. 

This  allowance  for  compression  and  clearance  may  be  cal- 
culated by  the  following  method  : 

Locate  the  point  T  on  the  diagram  where  the  expansion 
line  would  have  terminated,  provided  the  steam  had  not  been 
released  until  the  end  of  the  stroke. 

Draw  the  line  T.  2,  parallel  with  the  atmospheric  line  A. 
A,  which  will  intersect  the  compression  curve  at  i,  at  which 
point  the  quantity  of  steam  exhausted  from  the  clearance  has 
been  restored ;  therefore  the  consumption  will  be  as  much  less 
than  the  rule  shows,  as  the  line  T.  i.  is  shorter  than  the  line 
T.  2,  or  the  length  of  the  diagram. 

Multiply  the  result  obtained  by  the  rule,  by  the  length  of  the 
line  T.  i,  and  divide  the  product  by  the  length  of  the  line  T.  2  ; 
the  result  will  be  the  rate  of  consumption  corrected  for  both 
clearance  and  compression. 

Example:  The  length  of  line  T.  i,  is  3.47  inches,  and 
the  length  of  line  T.  2,  is  3.75  inches.  The  rate  of  consump- 
tion obtained  by  the  rule  is  23.17,  hence  2317x3.47-^3.75  =  - 
21.43  pounds;  the  corrected  rate  per  indicated  horse  power  per 
hour. 

This  latter  method  is  most  generally  employed  by  engin- 
eers in  charge  of  plants,  as  it  gives  a  very  close  approximation, 
and  is  very  much  more  convenient  than  computations  made 
from  the  steam  displacement  of  the  cylinder. 

Where  diagrams  are  taken  that  have  only  a  small  amount 
of  compression,  the  line  T.  i,  will  not  intersect  the  compression 


And  Its  Appliances. 


161 


curve;  as  in  Fig.  78.     In  such  cases  it  is  necessary  in  order  to 
find  the  length  of  the  line  T.  i,  to  continue  the  curve  from  the 


FIG.  78. 

end  of  the  diagram,  (being  guided  by  the  eye)  upward  in  about 
its  natural  direction,  and  far  enough  beyond  the  end  of  the 
diagram,  as  to  be  intersected  by  the  line  T.  i,  which  is  always 
drawn  parallel  with  the  atmospheric  line,  as  shown  by  the 
dotted  lines  in  Fig.  78. 

The  line  T.  i,  will  therefore  be  lengthened,  but  whatever 
may  be  its  length,  it  is  always  the  multiplier  in  making  the  cor- 
rections, while  T.  2,  is  always  the  divisor,  and  represents  the 
length  of  the  diagram. 

In  this  case  the  result  obtained  by  the  rule  is  increased, 
because  the  multiplier  T.  i,  is  longer  than  T.  2. 

In  diagrams  like  Fig.  79  where  there  is  no  compression, 
the  proper  position  for  point  i  on  the  terminal  pressure  line 
may  be  found  as  follows :  First  draw  the  vacuum  line  V,  and 
locate  the  clearance  line  C,  in  accordance  with  the  best  data  at 
hand ;  then  draw  the  terminal  pressure  line  extending  from 


1 62 


Steam  Engine  Indicator 


T,  to  C,  which  will  intersect  the  end  of  the  diagram  at  point  2, 
and  from  point  2,  draw  a  diagonal  line  to  the  intersection  of 
clearance  line  with  the  vacuum  line ;  (see  2  V). 


FIG.  79, 

This  diagonal  will  intersect  a  continuation  of  the  back 
pressure  line  at  F,  directly  under  the  proper  place  for  point  i, 
on  the  terminal.  In  this  case  as  in  Fig.  78,  the  result  ob- 
tained from  the  rule  will  be  increased,  because  the  multiplier 
(distance  T.  i.)  is  longer  than  T.  2  in  the  correction. 

A  knowledge  of  existing  clearance  is  necessary,  as  such 
diagrams  give  no  information  in  regard  to  it.  But  the  expan- 
sion curve  of  a  cut-off  diagram  however,  does  furnish  the  in- 
formation necessary  to  arrive  at  approximately  at  the  volume 
of  clearance,  unless  the  curve  is  very  irregular  in  its  forma- 
tion. Diagram  Fig.  50  illustrates  the  method  of  establishing 
the  clearance  line  by  means  of  the  expansion  curve. 

The  diagram  Fig.  80  illustrates  one  process  of  locating 
the  point  i,  (T.  i.)  in  the  terminal  line,  when  this  line  is  be- 
low the  atmospheric  line,  and  consequently  below  any  part  of 
the  compression  curve  defined  on  the  diagram. 


A  nd  Its  Appliances 


Locate  the  terminal  line  by  drawing  from  T,  (the  terminal 
pressure)  a  line  parallel  with  the  atmospheric  line  and 
intersecting  the  end  of  the  diagram  at  2.  Select  any  point  in 
the  compression  curve  as  at  D. 


FIG.  80. 

From  that  point  draw  a  line  perpendicular  to  the  atmos- 
pheric line  to  terminal  line  as  at  F.  Then  from  V  where  the 
clearance  line  intersects  the  vacuum  line,  draw  a  diagonal  line 
through  point  F,  to  point  E,  (same  height  as  point  D.)  then  a 
line  drawn  perpendicular  to  the  atmospheric  line,  from  E,  will 
intersect  the  terminal  line  at  the  proper  place  for  point  i. 

The  process  will  be  recognized  the  same  in  principle  as 
that  used  for  finding  a  point  in  the  isothermal  expansion 
curve. 

The  water  consumption  computed  for  diagram  Fig.  80  is 
as  follows : 

The  mean  effective  pressure  as  measured  by  planimeter  is 
2J/&  pounds  per  square  inch,  and  the  terminal  pressure  is  7 
pounds  absolute. 


164  Steam  Engine  Indicator 

The  volume  for  7  pounds  as  given  in  the  Table  No.  8, 

is  3300,  hence      850375  ,  1  f 

Jyj/  J =  122.5  pounds  uncorrected  for  com- 
pression.           3300X2.125 

Line  T.  i,  is  2.60  inches  long,  and  lineT.  2C(or  the  whole 
length  of  diagram)  is  3.75  inches,  hence  122.5x2.60^-3.75  = 
84.93  pounds  per  indicator  horse  power  per  hour,  the  correct 
rate. 

Diagrams  similar  to  Fig.  80  are  wasteful  of  steam,  and  are 
usually  obtained  from  engines  having  insufficient  load,  and  a 
comparison  of  the  water  consumption,  (as  computed)  with  that 
of  diagrams  taken  from  moderately  loaded  engines  will  a.t  once 
make  apparent  the  economy  of  the  latter,  as  against  the  extrav- 
agant waste  of  the  former. 

..Probabtyinoi other  single  condition  is  so  detrimental  to 
good  economy  as  an  engine  over  large  for  its  work,  as  a  too 
light  load  necessitates  an  early  cut  off;  the  expansion  and  con- 
sequent fall  of  temperature  becomes  excessive,  and  hence  in- 
ternal condensation  appears  to  the  fullest  extent. 

In  the  computation  for  water  consumption  of  these  dia- 
grams it  must  be  understood  that  the  rates  as  calculated  are 
theoretical,  and  assumes  perfect  conditions,  such  as  dry  steam, 
entire  absence  of  loss  from  leakage,  condensation,  etc. 

The  diagram,  shows  only  the  minimum  amount  of  steam 
that  has  been  consumed  by  the  engine  to  do  a  given  amount  of 
work,  and  there  are  many  reasons  why  this  consumption  of 
water  as  shown  by  the  indicator  should  be  less  than  the  actual 
amount. 

It  is  considered  that  the  percentage  of  loss  in  a  modern 
and  properly  constructed  steam  plant  is  fully  twenty  per  cent.  ; 
and  taking  the  engine  alone,  is  at  least  ten  per  cent,  and  this 
may  be  still  further  increased  by  condensation,  and  also  where 
considerable  leakage  occurs,  etc.,  so  that  it  is  safe  to  add  at 
least  10  per  cent,  to  the  indicated  consumption  to  closely  ap- 
proximate the  actual  consumption. 


A  nd  Its  Appliances .  165 

The  loss  from  water  that  is  carried  over  with  the  steam  is 
chargeable  to  the  boiler,  and  not  to  the  engine.  \ 

The  unindicated  loss  will  also  be  greatest  at  light  loads. 
With  steam  at  80  pounds  pressure,  and  a  mean  effective  pres- 
sure of  from  about  40  to  45  pounds,  (corresponding  to  about 
one-fourth  cut-off),  will  give  the  least  loss. 

Very  short  cut-off  gives  an  increased  loss. 

The  steam  used  in  the  low  pressure  cylinders  of  compound 
engines,  first  passes  through  the  high  pressure  cylinder ;  hence 
the  water  consumption  as  computed  for  the  high  pressure 
cylinder,  (corrected  for  compression")  will  be  the  measure  of 
consumption  for  the  whole  engine. 

This  amount  is  to  be  divided  by  the  horse  power  of  the 
whole  engine  for  the  consumption  per  indicated  horse  power 
per  hour. 

The  consumption  may  also  be  computed  from  the  low 
pressure  cylinders  in  the  same  manner  as  for  the  high  pres- 
sure cylinder ;  but  which  will  be  found  to  disagree  with  the 
former  owing  to  some  loss  between  the  cylinders. 

It  will  also  be  found  that  if  no  other  steam  is  admitted  to 
the  low  pressure  cylinders,  except  what  has  already  passed 
through  the  high  pressure  cylinder,  that  the  water  consump- 
tion will  appear  greatest  when  calculated  from  the  high  pres- 
sure, and  will  gradually  become  less  from  each  successive 
cylinder:  therefore  it  is  a  good  plan,  and  of  interest  to  meas- 
ure the  consumption  from  each  and  all  of  the  cylinders,  and 
compare  the  results. 

The  differences  may  be  considered  as  fair  measures  of  the 
loss  in  transmission  between  the  cylinders. 

Another  method  is  here  given  for  calculating  the  water 
consumption  by  constant,  and  which  is  also  independent  of  any 
knowledge,  (except  the  mean  effective  pressure)  of  the  size  or 
speed  of  the  engine ;  and  which  may  be  easily  and  accurately 
determined  from  the  diagram,  for  both  cut-off,  and  release  by 


1  66  Steam  Engine  Indicator 

means  of,  and  the  use  of  the  formula  :  ..,   IT       X  (proportional 

M.  il/.  r. 

volume  at  cut-off  X  weight  of  steam)  minus,  (proportional  vol- 
ume at  compression  X  weight  of  steam)=  number  of  pounds 
of  steam  accounted  for  at  cut-off,  per  indicated  horse  power 
per  hour. 


Or,    by  the   formula  :        tf       X  (proportional   volume    at 

release  X  by  weight  of  steam)  minus,  (proportional  volume  at 
compression  X  weight  of  steam)  =  number  of  pounds  of  steam 
accounted  for  at  release  per  indicated  horse  power  per  hour. 

The  following  is  the  explanation  of  the  above  formula  : 

M.  E.  P.  is  the  mean  effective  pressure.  In  compound, 
triple  and  quadruple  expansion  engines,  this  is  the  sum  of  two 
or  more  quantities. 

One  is  the  M.  E,  P.  o'f  the  cylinder  under  consideration, 
as  for  instance,  the  high  pressure  cylinder,  and  the  others  are 
the  M.  E.  P.  in  the  other  cylinders  referred  to  the  high  pres- 
sure cylinder. 

The  proportional  volume  at  cut-off  is  the  percentage  of  the 
stroke  computed  at  cut-off,  (as  at  D.  Fig.  81)  added  to  the  per- 
centage of  clearance,  and  this  is  to  be  multiplied  by  the  weight 
of  one  cubic  foot  of  steam  at  the  cut-off  pressure. 

The  proportional  volume  at  compression  is  the  percentage  of 
the  return  stroke  uncompleted  at  compression  added  to  the 
percentage  of  clearance,  and  this  is  to  be  multiplied  by  the 
weight  of  one  cubic  foot  of  steam  at  the  pressure  where  com- 
pression begins. 

The  proportional  volume  at  release  is  the  percentage  of 
the  stroke  completed  at  release  added  to  the  percentage  of 
clearance,  and  this  is  to  be  multiplied  by  the  weight  of  one 
cubic  foot  of  steam  at  the  pressure  where  release  is  taken. 

The  constant  1375013  the  volume  of  steam  in  cubic  feet 
per  hour  required  by  an  engine  without  clearance  to  develop 


A  nd  Its  Appliances.  1 6 7 

one  horse  power  when  working  with  one  pound  pressure  per 
square  inch  and  without  expansion.  This  quantity  will  be 
less  in  proportion  to  the  increase  of  average  pressure ;  there- 
fore it  is  divided  by  the  mean  effective  pressure  (M.  E.  P.)  of 
the  diagram. 

The  quantity  will  also  be  increased  in  proportion  to  the 
percentage  of  clearance,  and  decreased  by  the  quantity  of  steam 
saved  by  compression. 

The  points  of  cut-off,  release,  and  compression  referred  to 
are  shown  respectively  at  D.  E.  and  F.  in  the  diagram  Fig.  81. 


FIG.  81. 

The  pressures  at  these  points  must  be  the  absolute  pres- 
sure, taken  from  zero  or  a  perfect  vacuum,  which  is  14.7 
pounds  below  the  atmosphere  when  the  barometer  indicates 
29.92  inches. 

Where  great  accuracy  is  desired,  the  height  of  the  barom- 
eter should  be  observed,  when  the  diagrams  are  taken  in  order 
that  the  atmospheric  pressure  which  it  shows  should  be  used 
in  such  cases. 


1  68  Steam  Engine  Indicator 

The  pressure  of  the  atmosphere  as  shown  by  the  barome- 
ter in  inches  of  mercury  should  be  multiplied  by  0.491  to  re- 
duce it  to  pounds  per  square  inch. 

The  requisite  data  for  computing  the  amount  of  steam  ac- 
counted for,  from  the  diagram  Fig.  81  is  as  follows:  The  pro- 
portion of  stroke  completed  at  cut-off  D,  is  thirty-hundredths, 
(.30)  and  the  absolute  pressure  of  steam  per  square  inch  at  that 
point  is  eighty-three  (83)  poundSo 

The  weight  of  a  cubic  foot  of  such  steam  is  .1967  pounds. 

The  proportion  of  stroke  completed  at  release  E,  is  ninety  - 
hundredths  (.90)  and  the  absolute  pressure  thirty  (30)  pounds. 

The  weight  of  a  cubic  foot  of  such  steam  is  .0755  pounds. 

The  proportion  of  the  return  stroke  uncompleted  at  com- 
pression F.  is  ten-hundredths  (.10)  the  absolute  pressure  is 
sixteen  (16)  pounds,  and  the  weight  of  a  cubic  foot  of  this 
steam  is  .0413  pounds. 

The  clearance  of  the  engine  equals  .02  per  cent. 

The  mean  effective  pressure  on  the  piston  is  forty  (40) 
pounds  per  square  inch.  Hence  by  this  method  the  amount  of 

steam  accounted  for  at  cut-off  will  be    3'^     x(.3Q+-°2)-  1967  — 

40 

(.10-)-.  02).  0413  =  343.  75  X  .0579=  19.90  poundsof  steam  or  water 
per  indicated  horse  power  per  hour. 

The   amount   of   steam   accounted  for  at  release  will  be  : 

—  (.  io+.  02).  041  3  =  343.  75  X.  0645  =  22.  1  7 


40 
pounds  of  steam  per  hour. 

Suppose  in  the  engine  to  which  these  calculations  ap- 
ply, an  actual  feed  water  test  gave  a  consumption  of  thirty 
(30)  pounds  of  water  per  indicated  horse  power  per  hour; 
then  the  percentage  of  feed  water  accounted  for  at  cut-off  is 

10.90  22.17 

^  ^  =.663  and  at  release  -  i-=. 


A  nd  Its  Appliances. 


169 


The  formula  for  release  may  be  simplified  in  cases  where 
there  is  a  sufficient  amount  of  compression,  by  locating  the 
compression  point  at  such  a  height  on  the  compression  curve  as 
will  make  that  pressure  and  the  release  pressure  equal,  as 
shown  in  diagram  Fig.  82. 

The  formula  then  becomes        L^      (percentage  of  stroke 

completed  at  release,  minus  percentage  uncompleted  at  com 
pression)  multiplied  by  the  weight  of  a  cubic  foot  of  steam  at 

release  pressure,  thus,         -p   p  (-90— .io).O755  =  2O.62  pounds, 

the  effect  of  clearance  disappearing.  The  quantity  in  the 
parenthesis  is  the  proportion  which  the  distance  (1)  between 
the  points  in  Fig.  82  bears  to  the  whole  length  of  the  diagram 


FIG. 


or  to  L.     That  is  the  proportion  1        ,_,.          ...  -  ... 

,  -^p-     This  applies  only  to  the 

release  formula.  .  L 


The  calculation  of  the  quantity      3/5 

M.  rj.  r. 


these  formulas 
may  be  facilitated  by  reference  to  following  Table   No.    5, 


Steam  Engine  Indicator 


QUANTITY    OP    STEAM    ACCOUNTED    FOR    BY 
INDICATOR. 


M.E.P. 
Ibs. 

13750 
M.E.P. 

M.E.P. 
Ibs. 

13750 
M.E.P. 

M  E.P. 

13750 

M.EjT 

M.E.P. 
Ibs. 

13750 
M.E.P. 

IO. 

1375,0 

36.5 

376.8 

66. 

208.3 

119. 

"5-5 

10.5 

1309-6 

37- 

37J  6 

6.7. 

205.2 

120, 

114-5 

ii. 

"•5 

I25P.O 
1195.6 

Is 

366.7 
361.9 

69!' 

2O2  .'2 
199-3 

121. 

122, 

113.6 
II2.7 

12. 

II45.8 

38.5 

357-2 

196  4 

1^23 

in.  7 

12.5 

IIOO.O 

39 

352.6 

7ii 

193-7 

124. 

1  10  8 

'3-5 

1057  7 
1008.6 

39-5 
40. 

3482. 
3438 

72. 

73 

I9I.O 

188  4 

no  o 
/°9-  * 

982.1 

40.5 

339-6 

74> 

185.8 

127. 

Vio8  2 

15- 

948.2 

4ii5 

335  4 
331  4 

'4: 

183,3 
180.9 

128. 
129. 

107  4 
106.5 

'5-5 
16. 

.887  'I 
859-4 

42. 
42  5 

327-4 
323-6 

w. 

1/8.6 
176-3 

130. 

105  ..7- 
104.9 

16  5 

833  ,4 

43- 

319  8 

79- 

174.1 

I32i 

104  i 

rt'-s 

808.^ 
785.8 

43-5 
4*4  v 

316  o 
312.6 

80. 
81. 

i6g!8 

133. 

103  3 

102.6 

18. 

763  9 

44^5 

309:o 

82. 

167:7 

*35. 

101.8 

18.5 

743  '2 

45- 

3P5-6 

83. 

^65  7 

136. 

101  .  i 

19* 

723.7 

45-5 

302  .  2 

84. 

163.7 

1.37- 

100.3 

»9-5 

7^5  * 

46. 

298.9 

85- 

161.8 

138. 

99.6 

20. 

687.5 

46.5 

295  6: 

86. 

J59-9 

139. 

98.9 

20  5 

670.8 

47- 

292.6 

87. 

158.0 

140. 

98.2 

21. 

21-5 
22, 

^S4? 
639.6 

625.0 

47  5 
48. 
48.5 

289.4 
286.5 

283  6 

88, 
90. 

156.2 

w-s 

152.8 

141. 

142. 
143- 

97-5 
96  8 
96.1 

22.5 

6y  .2 

49 

280.6 

91. 

151.1 

144. 

95-4 

23-, 
23.5 

597-8 
585-2 

49  5 
50. 

277-8 
275.0 

92. 
93- 

149.4 
147.8 

145- 
146. 

948 
94-1 

24. 

572-9 

50.5 

272  3 

94- 

146.3 

147- 

93.5. 

24-5 
25. 

561  2 
550.0 

51 

51-5 

269  6 
267  o 

1: 

144.7 

143   2 

148. 
149- 

,92.9 
'92.2 

25.5 

539  2 

52. 

264  4 

I4I.8 

150. 

91.6 

.20. 

528.9 

52-5 

261.9 

98. 

1403 

91.0. 

26.5 

518.8 

53 

259.4 

99- 

J38.9 

"152! 

90.4 

27. 

509  3 

53-5 

257  o 

100. 

153- 

89;8 

27  5 

500  o 

54- 

254.6 

101. 

^36'  I 

89.2 

28. 

49  r  i 

54  5 

252  3 

102. 

134.8 

155'. 

88.7 

28.5 

482-4 

55 

250  o 

103. 

133-4 

156. 

88...I 

29. 

474  * 

55  5 

247.7 

104. 

132.2 

157. 

87.5 

29  5 

466/2 

56. 

245-5 

IO5. 

130.9 

158. 

87.0 

30 

458.3 

56.5 

242.4 

106. 

129.7 

159. 

86,,'4 

30.5 

4508 

57- 

241.2 

107. 

128  5 

160. 

85,0 

3i  is 

443-5 
436.6 

57-5 
58- 

239- 
237 

108. 
109. 

127.3 
126.1 

161. 
162. 

slit 

,32. 

429  7 

58.5 

235- 

125.0 

163. 

84.3 

32-5 

423.0 

59 

233-  . 

in. 

123.8 

164, 

83.8 

33- 

416.7. 

231. 

112. 

122.7 

83.3 

33-5 

410.4 

60. 

229.2 

1I3. 

121.  6 

166. 

82.8 

34- 

404.5 

61. 

225  4 

114 

'120  6 

167, 

82.3 

34-5 
35. 

398*6; 

62, 
63: 

221    7 

218.3 

"i 

116. 

'"9-5 
118  5 

^69! 

81.8 
81.3 

j§:5 

387.4  ; 
381.9. 

64 
65- 

214.9 

3U.  5 

118. 

117.5 
116.5 

I7oi 

80.8 
80.4 

And  Its  Appliances. 


171 


QUANTITY    OF    STEAM     ACCOUNTED    FOR    BY 
INDICATOR.-Continued. 


M.E.P. 
Ibs. 

13750 

M.E.P. 
Ibs. 

13750 

M.E.P. 
Ibs. 

13750 

M.E.P. 

M.E.P. 
Ibs. 

13750 

M.E.P. 

M.E.P. 

M.E.P. 

172. 

79-9 

193- 

71.2 

213 

64.5 

233. 

59-0 

173- 

79-4 

194. 

70  8 

214. 

64   2 

234. 

5|.7 

174. 

79  ° 

195. 

70.5 

"I' 

63  9 

235  • 

Sf.S 

IB: 

78  5 
78.1 

197. 

70.1 
69.7 

216. 

217. 

636 
63.3 

237^ 

58  2 
58.0 

177. 

77.6 

198. 

69.4 

218. 

63.0 

238. 

57-7 

178. 

77#2 

199. 

69.0 

219. 

62.7 

239. 

57-5 

IB: 

76'3 

200. 

201. 

68^4 

220. 
221. 

625 
62.2 

240 
.     241. 

57-2 

181. 

75-9 

2O2. 

68.0 

222. 

61.9 

242. 

s&S 

182. 

75-5 

203. 

67.7 

223 

61  6 

243- 

56.5 

183.. 

75-1 

204. 

674 

224. 

61  3 

244. 

56  i 

184. 

IS: 

74  7 
74-3 
73  9 

20|. 
206. 
207. 

66!  7 
66  4 

225. 
226. 
227 

61  I 

60.8 
605 

245- 
246. 
247. 

5S"8 
55  6 

73  5 

208 

66.1 

228. 

60.3 

248. 

55  4 

Iss! 

209. 

65.7 

229. 

60  o 

249. 

55-2 

189. 

72  7 

2IO. 

65.4 

230. 

59-7 

250 

55-0 

190. 

72-3 

211. 

65.1 

23L 

59-5 

251  • 

54-7 

19?. 

71.9 

212. 

64.8 

232. 

59-2 

252. 

54.5 

192. 

71.6 

The  foregoing  table  gives  the  result  of  the  division  for 
each  half  pound  mean  effective  pressure,  between  10  and  60, 
and  for  each  pound  between  60  and  252. 

It  is  a  good  plan  to  compute  the  steam  accounted  for,  at 
both  cut-off  and  the  release  points  of  the  diagram ;  because  if 
the  expansion  curve  should  deviate  much  from  the  isothermal 
a  very  different  result  is  shown  at  one  point  from  that  shown 
at  the  other. 

In  many  cases.the  extent  of  the  loss  occasioned  by  cylin- 
der condensation  and  leakage  is  indicated  in  a  more  truthful 
manner  at  the  cut-off  than  at  release. 

The  constant  13750  may  also  be  employed  in  a  somewhat 
similar  manner  for  computing  the  steam  consumption  of  an 
engine,  by  the  following  method. 

Select  any  point  as  at  D.  on  the  expansion  curve,  Fig.  83, 
and  draw  a  line  from  it,  and  parallel  with  the  vacuum  line, 


172 


Steam  Engine  Indicator 


until  it  intersects  the  compression  line  at  C,  then  with  the  scale 
of  the  spring,  (measuring  from  vacuum  to  the  height  of  this- 
line  above). find  the  pressure  of  steam  at  such  height;  then 
-from  Table  No.  8,  find  the  weight  of  a  cubic  foot  of  steam  at 
that  pressure. 


FIG.  83. 

Multiply  13750  by  this  weight  of  steam  per  cubic  foot,  and 
by  the  distance  in  inches,  between  the  points  C.  and  D.  Di- 
vide the  product  by  the  mean  effective  pressure  multiplied  by 
the  distance  A.  A.  or  the  extreme  length  of  the  diagram. 

The  result  will  be  the  number  of  pounds  of  steam  con- 
sumed per  indicated  horse  power  per  hour  as  shown  by  the 
diagram. 

For  example :  Suppose  the  whole  length  of  the  diagram 
to  be  3.75  inches,  and  the  distance  between  the  points  C.  and 
D,  3.10  inches,  the  scale  of  the  spring  40,  and  the  mean  effect- 
ive pressure  39  pounds  per  square  inch,  the  pressure  from  va- 
cuum to  line  C.  D.  being  30  pounds.  The  weight  of  a  cubic 
foot  of  this  steam  as  shown  by  the  table  No.  8  is  .0755  pounds. 


A  nd  Its  Appliances.  1 7  3 

Therefore    I375°X.   755X3- — —  22.    pounds  consumption  per 

39X3-75 
indicated  horse  power  per  hour. 

The  use  of  the  constant  number  13750  is  based  on  the  fol- 
lowing considerations : 

If  a  piston  one  square  inch  in  area  moves  twelve  inches, 
it  will  do  work  equal  to  one  foot  pound  for  each  pound  pressure 
of  steam  per  square  inch.  That  is,  every  twelve  cubic  inches 
of  piston  displacement  represents  one  foot  pound  of  work  at 
one  pound  mean  effective  pressure  ;  and  as  twelve  cubic  inches 
is  equal  to  TJT  of  a  cubic  foot,  the  piston  must  sweep  a  volume 

of  33QQ°X6o  _  cubic  feet  per  horse  power  per  hour,  when 

144 

the  mean  pressure  equals  unity ;  therefore  as  the  volume  of 
steam  used  per  horse  power  per  hour  varies  inversely  as  the 
mean  effective  pressure  and  if  the  weight  of  a  cubic  foot  of 
steam  at  the  release  pressure  be  designated  by  W,  and  the 
mean  effective  pressure  by  M.  E.  P.  we  have  the  formula, 

_LlZ5p_xW_ the  number  of  pounds  of  water  consumed  per 
M.  E.  P. 

indicated  horse  power  per  hour,  exclusive  of  waste  by  condens- 
ation and  leakage ;  and  also  makes  no  allowance  for  clearance 
and  compression. 


Steam  Engine  Indicator 


CHAPTER  XXII. 


INDICATOR   TESTING   DEVICE. 


In  indicator  practice  it  is  frequently  found  that  the  initial 
pressure  in  the  steam  cylinder,  as  shown  by  the  indicator  dia- 
gram, will  in  some  cases  be  from  five  to  ten  or  twelve  pounds 
less  pressure  per  square  inch,  than  the  pressure  in  the  boiler, 
as  indicated  by  the  steam  guage. 

This  discrepancy  in  pressure  between  the  indicator  and 
steam  guage  may  arise  from  various  causes ;  such  as  inadequate 
size  of  steam  pipe,  also  tortuous  and  rough  passages,  non- 
covered  or  unprotected  pipes,  incorrect  valve  setting,  tardy 
valve  motion,  etc. ;  all  or  any  of  which  tend  to  cause  an  appar- 
ent difference  of  pressure  between  the  indicator  and  steam 
gauge. 

Where  such  differences  do  exist  in  these  pressures,  the 
fault  is  generally  supposed  at  first  thought,  to  lie  with  the  in- 
dicator, when  in  fact  it  may  be  due  to  any  of  the  causes 
named ;  or  may  be  due  to  the  incorrectness  of  the  steam  gauge 
itself. 

Therefore  it  becomes  important  that  means  be  taken  to 
ascertain  how  near  the  gauge  and  indicator  agree  in  denoting 
the  steam  pressure,  in  order  that  the  amount  of  pressure  lost 
between  the  boiler  and  engine  may  be  determined. 


And  Its  Appliances. 


175 


For  making  such  comparative  tests  the  arrangement  illus- 
trated in  Fig.  84,  is  easily  constructed,  not  very  expensive, 
and  is  well  adapted  for  the  purpose. 

It  may  be  connected  directly  with  the  steam  space  of  the 
boiler,  or  may  be  attached  to  the  steam  pipe  in  any  convenient 
position. 


FIG.  84. 


In  making  a  comparative  test  when  the  device  is  attached 
to  the  steam  pipe  (as  shown)  it  is  best  that  it  be  done  at  a  time 
when  the  engine  is  at  rest,  and  the  throttle  valve  closed  in  or- 
der to  avoid  any  fluctuations  of  pressure  that  otherwise  might 
exist  in  the  pipe. 


176  Steam  Engine  Indicator 

In  the  matter  of  construction  the  Chamber  C.  should  be  of 
such  size  as  to  contain  a  considerable  volume  of  steam,  and 
such  chamber  may  consist  of  an  ordinary  four  inch  cross  fitting, 
with  the  inlet  and  outlets  reduced  to  suit  the  size  of  pipe  em- 
ployed. 

Steam  is  admitted  to  the  system  through  a  i  inch  pipe, 
and  controlled  by  the  globe  valve  A,  and  discharged  as  occa- 
sion requires,  through  the  ij{  inch  pipe  by  the  valve  D.  This 
pipe  is  made  larger  in  order  to  facilitate  the  discharge  of  the 
volume  of  steam  under  pressure  in  the  chamber,  as  quickly  as 
possible. 

The  top  is  tapped  to  suit  the  indicator  cock  I,  which  is  us- 
ually made  of  a  size  corresponding  to  ]/2  inch  pipe  fittings. 

The  bent  pipe  U,  leading  to  the  steam  guage  G,  may  be 
of  y±  inch  pipe. 

The  bend  in  the  guage  pipe  should  be  extended  downward 
at  least  four  or  five  feet  below  the  center  of  the  four  inch  cross 
fitting;  thereby  securing  a  sufficient  column  of  water  to  insure 
against  overheating  of  the  gauge  above  the  existing  medium, 
or  atmosphere. 

Before  preparations  for  any  tests  are  made,  it  will  be 
advisable  to  partly  fill  the  gauge  pipe  with  water ;  which  can 
be  readily  accomplished  by  disconnecting  the  gauge  G,  and 
pouring  water  into  the  pipe  until  it  stands  in  both  legs  of  the 
pipe  about  as  high  as  the  center  of  the  chamber  C. 

In  preparing  to  make  a  test,  attach  the  indicator  contain- 
ing its  spring,  and  also  steam  guage,  in  the  manner  shown  in 
the  illustration,  and  secure  a  piece  of  paper  in  the  usual  way 
to  the  drum  of  the  indicator.  Close  the  discharge  valve  D,  and 
open  the  indicator  cock  I,  also  open  communication  between 
indicator,  and  gauge,  by  means  of  cock  F. 

Now  by  gradually  admitting  steam  to  the  chamber  by  the 
valve  A,  there  will  be  a  simultaneous  advance  movement  of 
both  the  indicator  pencil,  and  gauge  hand,  and  which  will 


A  nd  Its  Appliances.  1 77 

continue  as  the  steam  is  admitted  until  the  desired  limit  of  the  in- 
dicator spring  has  been  reached.  This  is  a  preliminary  oper- 
ation for  the  purpose  of  warming  up  the  indicator  preparatory 
to  making  the  card. 

After  the  indicator  and  its  spring  has  been  thoroughly 
warmed,  first  close  the  valve  A,  and  then  open  the  valve  D, 
thus  discharging  the  steam  from  the  chamber,  through  the 
open  pipe  into  the  atmosphere ;  and  thus  lowering  the  pres- 
sure, and  causing  the  indicator  pencil  and  gauge  hand  to 
return  each  to  their  normal  positions. 

Now  with  one  hand,  bring  the  indicator  pencil  in  contact 
with  the  paper  on  the  drum ;  and  by  means  of  the  cord  E, 
(with  the  other  hand)  cause  the  drum  to  rotate  a  small  amount, 
which  in  consequence  results  in  tracing  a  line  upon  the  paper, 
and  which  represents  the  zero  or  atmospheric  line. 

Then  close  the  discharge  valve  D,  and  slowly  admit  steam 
to  the  chamber  through  the  valve  A,  and  continue  until  the 
observed  reading  of  the  steam  gauge  denotes,  say  ten  pounds 
pressure  per  square  inch. 

Just  at  this  point  mark  another  line  on  the  paper  by  the 
same  means,  (by  hand)  as  employed  in  tracing  the  atmospheric 
line. 

Continue  to  mark  the  corresponding  lines  on  the  paper  for 
each  successive  ten  pounds  movement  of  the  gauge  hand  (from 
observation)  until  the  pressure  limit  of  the  indicator  spring  has 
been  reached. 

Close  the  admission  valve  A,  and  discharge  the  steam  re- 
maining in  the  chamber  through  the  valve  D. 

Remove  the  paper  from  the  drum,  and  compare  the  mark- 
ing with  a  rule  or  scale,  on  which  the  divisions  coincide  with 
pounds  pressure  per  square  inch,  according  to  the  denomination 
of  the  indicator  spring  used. 

Supposing  a  forty  pound  spring  is  to  be  used  in  the  indi- 
cator, and  assuming  both  the  steam  gauge  and  spring  as 


178  Steam  Engine  Indicator 

correct ;  then  the  marking1  would  appear  as  shown  at  A  in  the 
illustration  Fig.  85  for  each  ten  pounds  on  the  gauge,  succes- 
sively from  zero  to  eighty  pounds  pressure  per  square  inch. 
But  in  many  cases  they  do  not  agree  so  uniformly,  as  shown 
in  the  figure  from  the  fact  than  steam  gauges,  and  also  indica- 
tor springs  vary  more  at  some  pressures,  than  at  others; 
hence,  such  a  test  enables  the  operator  to  observe  the  true  ac- 
tion of  the  spring;  also  at  what  part  of  the  marking  the  great- 
est variations  (if  any)  occur,  and  shows  that  some  springs 
although  correct  in  some  parts  of  their  compression,  are  incor- 
rect in  other  parts ;  and  also  that  either  gauge  or  spring  may 
show  light  at  some  pressure  and  heavy  at  another. 

If  the  spring  registers  the  greater  pressure  according  to 
its  scale  it  is  light,  and  if  less  it  is  heavy,  provided  the  steam 
gauge  is  correct. 

This  device  is  easily  manipulated  to  mark  a  descending, 
as  well  as  an  ascending  pressure,  and  on  the  same  paper,  and 
may  be  accomplished  by  a  very  gradual  releasing  of  the  pres- 
sure in  the  chamber,  after  the  extreme  height  (to  which  the 
indicator  spring  should  be  subjected)  has  been  reached,  and  in 
again  marking  the  paper,  upon  the  descent  of  the  pencil,  from 
the  same  readings  of  the  gauge  as  was  done  in  the  ascending 
pressure. 

A  comparison  of  this  kind  is  both  interesting  and  instruc- 
tive, as  it  furnishes  the  means  for  observing  the  various  phe- 
nomina  connected  with  springs  in  general,  and  in  their  appli- 
cation to  different  purposes. 

In  a  test  of  this  description,  and  where  friction  exists  in 
the  indicator,  it  is  found  that  a  variation  or  lack  of  coincidence 
more  or  less,  appears  in  the  lines  so  marked ;  that  is,  a  differ- 
ence between  the  lines  marked  when  the  pencil  is  rising  and 
those  marked  when  the  pencil  is  under  falling  pressure ;  the 
latter  failing  (particularly  at  the  higher  pressures)  to  drop  suf- 
ficiently low,  as  to  meet  the  lines  marked  during  a  rising 


A  nd  Its  Appliances. 


179 


pressure :  A  corresponding-  pressure  always  being  denoted  by 
the  steam  gauge  at  each  marking  up  or  down. 

This  lack  of  coincidence,  gradually  decreases  from  the 
higher  pressures  downward  until  the  zero  line  has  been  reached, 
and  where  the  lines  again  agree. 

This  is  shown  at  B,  Fig.  85,  and  the  column  marked  up, 
is  the  rising,  and  that  marked  down  the  falling  pressure. 

The  fact  of  their  disagreement  is  caused  principally  to 
undue  friction  in  some  part  of  the  indicator,  and  might  also  be 


Tip 


Up       Down 


ou 
70 
60 
50 
40 
30 
20 
10 
0 

ou 
70 
60 
50 
40 
30 
20 
10 
0 

tJXJ 

70 
60 
56 
40 
30 
£0 
10 

B 


FIG.  85. 


partly  due  under  some  circumstances  to  lost  motion  in  the  pen- 
cil mechanism. 

Consequently  the  elimination  of  friction  in  the  indicator  to 
a  minimum,  is  a  matter  greatly  to  be  desired ;  it  being  an  im- 
portant requirement  in  all  indicators,  in  order  to  insure  accu- 
racy in  the  diagrams. 

Although  an  indicator,  upon  inspection  may  appear  satis- 
factory in  all  respects  when  cold,  it  may  become  the  reverse  of 
this  when  in  operation  and  subjected  to  a  high  temperature  of 
steam;  this,  application  of  heat,  and  circumstances  causing 


i8o  Steam  Engine  Indicator 

unequal  expansion  of  the  metals  of  which  the  indicator  cyl- 
inder is  composed. 

The  expansion  that  takes  place  upon  being  heated,  varies 
in  the  different  parts  of  the  indicator;  generally  increasing 
the  size  of  the  piston  to  a  greater  extent  than  it  does  the  sur- 
rounding metal ;  and  thereby  involves  a  liability  of  the  indica- 
tor piston  to  become  sufficiently  increased  in  size  as  to  bind  in 
the  cylinder ;  thus  creating  excessive  friction,  but  which  may 
obviously  be  eliminated  by  a  slight  reduction  in  the  size  of  the 
piston. 

Another  source  of  friction  which  often  happens,  arises 
from  springs  of  imperfect  construction,  or  out  of  true,  causing 
when  under  tension,  a  lateral  or  side  pressure  against  the 
cylinder. 

Either  of  these  faults  results  in  an  interrupted  or  broken 
action  in  the  movement  of  the  pencil,  and  which  is  fatal  to  the 
accuracy  of  the  instrument,  therefore  in  order  that  perfect 
freedom  of  action,  and  that  smoothness  and  accuracy  in  the 
pencil  movement  be  attained,  it  is  indispensable  that  friction  in 
the  instrument  be  reduced  to  the  lowest  degree  possible. 

By  the  use  of  this  device  an  amount  of  interesting  and 
varied  information  may  be  obtained,  pertaining  to  the  condi- 
tion and  action  of  springs,,  the  variations  in  pressure  for  equal 
movement  of  the  pencil,  in  showing  the  difference  between 
a  rising  and  falling  pressure  when  undue  friction  is  present, 
and  also  as  a  means  of  observing  inaccuracies  that  may  appear 
in  any  part  of  the  mechanism  connected  with  the  indicator. 

In  many  cases  errors  arise  from  excessive  friction  of  the 
indicator  piston,  caused  by  scale  or  grit  of  any  description 
being  carried  from  the  pipes  and  other  connections  leading 
to  it. 

If  such  should  be  suspected  it  will  likely  be  detected 
(where  slow  speeds  prevail)  either  by  close  observation  of  the 
pencil  in  its  movement  up  and  down,  or  by  placing  the  ringer 


And  Its  Appliances.  181 

at  the  top  of  the  indicator  piston  rod,  and  gently  follow  it  in 
its  downward  movement. 

As  a  matter  of  course  the  remedy  is  to  remove  the  piston 
and  clean. 

Sometimes  with  new  indicators  and  clean  pistons  an  un- 
usual amount  of  piston  friction  shows  itself  in  the  diagram  by 
a  series  of  very  definite  serrations  on  the  expansion  line  just 
after  cut-off,  as  shown  in  Fig.  86  the  horizontal  portion  of  the 
serrations  indicating  a  disposition  of  the  piston  to  hang  at  each 
of  these  positions  in  its  descent. 


FIG. 


In  some  cases  of  this  kind  it  may  be  necessary  to  very 
slightly  reduce  the  size  of  the  piston  by  means  of  a  fine  crocus 
paper,  or  by  oiling,  and  allowing  it  to  run  a  short  time,  having 
first  disconnected  the  pencil  movement. 

With  springs  of  a  higher  tension,  that  is,  with  stronger 
springs,  the  serrations  resulting  from  the  friction  of  a 
tightly  fitting  piston,  will  not  be  so  apparent,  and  will  be  less 
defined,  than  with  the  lighter  springs.  However  the  difference 
in  results  on  the  diagram  between  a  tight  piston,  and  one  fit- 
ting freely,  will  be,  that  with  the  former  the  various  events  of 
the  stroke  such  as  cut-off,  release,  and  compression,  will  occur 


1 82  Steam  Engine  Indicator 

later  in  the  stroke,  owing  to  the  tardy  response  of  the  piston 
to  the  variations  of  steam  pressure. 

The  fricton  of  a  tightly  fitting  piston  therefore  will  cause 
the  initial  pressure  to  be  /ess,  but  the  pressure  along  the  expan- 
sion, and  also  the  back  pressure  line,  (on  account  of  its  tardi- 
ness) will  be  greater,  than  with  the  more  freely  moving  piston. 

However  the  area  of  diagrams  from  each  may  not  differ 
greatly;  because  the  loss  of  initial  pressure  is  partially  com- 
pensated in  the  formation  of  the  expansion  line ;  owing  to  a 
tardy  piston. 

Occasionally  the  mean  effective  pressure  in  each  may  not 
differ  materially,  still  in  most  diagrams  that  have  been  taken 
with  an  indicator  in  which  the  piston  was  too  tightly  fitted,  the 
diagrams  have  been  found  to  be  unreliable,  inaccurate,  and 
misleading. 

The  piston  friction  on  an  indicator  may  be  approximately 
determined  in  the  following  manner :  First  allow  the  instru- 
ment (by  a  few  working  strokes)  to  become  heated  to  a  temper- 
ature coinciding  with  the  steam  pressure  present ;  then  after 
closing  communication  with  the  engine  cylinder,  gently 
depress  the  pencil  lever  (by  hand)  just  sufficient  to  slightly  ex- 
tend the  spring,  and  then  allow  it  to  slowly  return  to  rest. 

While  in  this  position  a  horizontal  line  is  drawn  on  the 
diagram. 

The  pencil  lever  is  next  raised  and  the  spring  slightly  com- 
pressed, and  then  again  allowed  to  come  to  rest  and  another 
line  drawn  as  before. 

The  distance  or  space  between  the  lines  so  marked  is  a 
measure  of  the  sum  of  the  total  frictional  resistance  in  both 
directions,  and  assuming  the  pencil  movement  without  friction, 
then  the  whole  of  the  error  so  measured  is  attributable  to  pis- 
ton friction. 

Careful  attention  to  the  lubrication  of  the  piston,  and  pen- 
cil movements  will  conduce  to  smooth  running,  and  to  a  certain 


A  nd  Its  Appliances.  3  S  3 

extent,    will   prevent   the   tendency   to   stick   or   bind  in  the 
cylinder. 

Clean  cylinder  oil  will  be  found  a  far  superior  lubricant 
for  the  piston,  than  the  limpid  oil  used  for  the  pencil  move- 
ments. 


^  I 

^ 


184  Steam  Engine  Indicator 


CHAPTER  XXIII. 


PLANIMETERS. 


Where  considerable  care  and  attention  is  used  the  mean 
effective  pressure  of  diagrams  may  be  computed  with  a  close 
approximation  to  accuracy,  by  the  use  and  method  of  ordinates, 
as  before  described,  but  the  operation  is  usually  attended  with 
considerable  anxiety,  and  also  becomes  otherwise  a  rather  tedi- 
ous operation  in  various  ways  with  more  or  less  liability  of 
error.  Therefore,  where  the  mean  effective  pressure  of  a  large 
number  of  diagrams  is  desired,  and  where  greater  accuracy  is 
required,  time  and  labor  may  be  greatly  facilitated  by  the  use 
of  an  instrument  termed  a  Planimeter,  constructed  and  used 
for  the  purpose  of  correctly  measuring  the  area  of  any  irregular 
figure  regardless  of  its  outline.  There  are  various  forms  of 
this  instrument,  some  of  which  are  so  constructed  that  by 
moving  the  tracing  point  over  the  entire  outline  of  a  diagram, 
its  area  may  be  read  from  a  graduated  index  wheel,  its  move- 
ment being  relative  to  some  fixed  or  zero  point.  There  are 
others  in  which  the  reading  is  taken  from  the  movement  of  a 
blank  wheel,  traversing  a  graduated  scale,  and  the  result  is 
ascertained  by  noting  the  coincidence  on  the  scale  of  some 
particular  line  corresponding  to  the  edge  of  the  wheel  that  has 
been  selected,  and  made  to  coincide  with  a  zero  point  of  the 
scale ;  when  commencing  to  trace  the  diagram. 

The  instrument  shown  and  illustrated  in  Fig.  87  is  one  of 
the  former,  with  a  graduated  index  wheel  and  vernier  and 


A  nd  Its  Appliances. 


185 


represents  the  well  known  Coffin  Averaging  Planimeter  in 
position  on  its  board ;  and  which  was  especially  designed  and 
adapted  to  the  purpose  of  measuring  the  mean  effective  pres- 
sure of  indicator  diagrams.  With  this  instrument  no  calcula- 

t  i  o  n  s  whatever 
are  required  to 
ascertain  the  av- 
erage pressure  or 
mean  height  o  f 
the  diagram 
throughout  the 
stroke  of  the  en- 
gine, and  it  may 
also  be  applied, 
when  desired,  for 
m  e  a  suring  the 
areas  of  any,  and 
all  other  irregu- 
lar figures.  It  is 
especially  valua- 
ble where  a  large 
number  of  dia- 
grams have  to  be 
measured  for  area 
or  mean  effective 
pressure,  either 

or  both  of  which  may  be  ascertained  at  all  times 
(without  any  adjustment  of  the  instrument),  by  a 
single  passage  of  the  tracing  point  around  the  outline  of  the 
figure.  In  consideration  of  the  accuracy  attained  and  the  ease 
with  which  it  is  manipulated  makes  its  use  desirable  in  all  cases 
in  a  single  as  well  as  in  a  number  of  diagrams,  as  the  chances 
of  error  in  making  calculations  are  entirely  eliminated. 


1 86  Steam  Engine  Indicator 

The  parts  of  this  instrument  being  permanently  secured  in- 
sures it  always  ready  for  use,  without  the  necessary  adjustment 
to  length  of  diagram,  etc.,  required  by  some  other  makes,  in 
order  to  ascertain  areas  and  average  pressures,  and  which  gives 
only  the  readings  of  one  or  the  other  separately.  This  instru- 
ment measures  the  area  and  average  pressure  or  mean  height 
of  any  diagram  or  figure  at  the  same  operation,  however  ir- 
regular, or  whatever  its  shape  may  be,  just  as  quickly  and 
accurately  as  if  it  were  some  regular  figure,  such  as  a  square 
or  rectangle. 

The  Coffin  Averaging  Instrument  proper  consists  of  an 
arm  fitted  at  one  end  with  a  tracing  point  O,  and  at  the  other 
with  a  hardened  steel  guide  pin  (not  shown  in  the  cut),  the 
centre  of  which  is  common  with  the  centre  of-  the  weight  Q. 
Upon  this  arm  is  also  mounted  a  graduated  index  wheel  and 
spindle,  delicately  poised  on  hardened  steel  centres,  thereby 
reducing  friction  to  a  minimum.  The  axis  of  said  wheel  being 
parallel  to  a  line  drawn  from  the  centre  of  a  guide  pin  to  the 
tracing  point.  In  close  proximity  to  the  wheel  there  is  per- 
manently secured  to  the  arm  a  graduated  vernier  scale  and 
used  in  connection  with  the  graduations  of  the  wheel,  thereby 
enabling  the  readings  to  be  readily  observed  in  small  fraction- 
al parts  of  a  square  inch.  The  distance  between  the  centres 
of  the  guide  pin  and  the  tracing  point  of  the  arm  is  assumed 
to  represent  the  length  of  one  side  of  a  rectangle,  while  the 
circumference  of  the  graduated  wheel  represents  its  component 
or  height,  and  if  the  terms  of  these  two  factors  be  in  inches, 
the  product  of  their  multiplication  will  be  the  area  of  the 
rectangle  of  such  dimensions  in  square  inches.  For  example : 
In  this  instrument  the  distance  between  the  guide  pin  and 
tracing  point  is  six  and  one-quarter  (6.25)  inches,  and  the  cir- 
cumference of  the  wheel  two  and  four-tenths  (2.4).  correspond- 
ing to  a  diameter  of  about  .764  part  of  an  inch,  then  6.25x2.4 
is  equal  to  fifteen  square  inches,  which  will  be  the  area  of  a 


A  nd  Its  Appliances  187 

rectangle,  where  one  of  its  dimensions  coincides  in  length,  with 
the  distance  between  the  guide  pin  and  tracing  point,  and  the 
other  with  the  circumference  of  the  graduated  wheel.  The 
circumference  of  the  wheel  is  therefore  divided  into  fifteen  (15) 
main  divisions,  each  division  representing  one  square  inch  area 
of  the  rectangle. 

Each  of  the  main  divisions  are  sub-divided  into  five  (5) 
equal  parts,  each  one  representing  one-fifth  (1-5)  or  twenty 
hundredths  of  a  square  inch.  The  vernier  scale  is  composed 
of  ten  ( i  o)  divisions,  their  combined  linear  distance  being  just 
equal  to  nine  (9)  subdivisions  of  the  wheel.  Therefore,  as  each 
subdivision  on  the  wheel  represents  one-fifth  (1-5)  or  twenty 
hundredths  (20)  then,  accordingly  the  divisions  of  the  vernier 
will  represent  eighteen  hundredths  (18)  a  difference  of  two 
hundredths  (02),  consequently  the  vernier  enables  the  sub- 
divisions to  be  read  to  one-fiftieth  (1-50)  or  two  hundredths 
(.02)  of  a  square  inch. 

Accompanying  the  instrument  is  a  nicely  finished  mahog- 
any board,  upon  which  it  is  mounted  when  in  use,  and  an 
especially  prepared  blank  card  is  firmly  secured  to  the  board 
upon  which  the  Index  Wheel  travels.  There  is  also  fitted  to 
the  board  a  metal  grooved  guide  I  in  which  the  guide  pin  slides 
being  secured  therein  by  the  weight  Q.  The  Clips  C  and  K 
are  for  the  purpose  of  securing  the  card  to  be  measured  in  the 
most  easy  and  convenient  position  for  the  operator.  The 
angle  clip  C  is  fixed  permanently  to  the  board  with  its  inner 
edge  in  a  direct  line  with  the  centre  of  the  groove  in  the  guide 
I.  The  clip  K  is  secured  to  a  slide  that  is  moveable  in  order 
that  it  may  be  adjusted  to  any  length  of  card.  The  guide  I  is 
secured  by  a  suitable  thumb  screw  on  the  under  side  of  the 
board ;  said  guide  is  shown  in  the  cut  with  its  end  projecting 
beyond  the  board,  which  is  its  proper  position  when  in  use. 
The  guide  may,  if  desired,  be  reversed  on  the  board  which 

bring  its  end  even  with  the  same,  and  affords  a  better 


1 88  Steam  Engine  Indicator 

opportunity  of  packing  or  laying  away  when  not  in  use.  In  pre- 
paring to  use  the  instrument  the  indicator  card  is  first  placed  un- 
der the  clips  C  and  K  which  are  so  made  as  to  admit  of  its  be- 
ing inserted  underneath  and  adjusted  in  the  proper  position, 
that  is,  with  the  extreme  left  hand  end  of  the  diagram  coincid- 
ing with  the  perpendicular  edge  of  the  clip  C,  while  the  atmos- 
pheric line  is  placed  near  to  and  parallel  with  the  horizontal 
edge  of  the  clip.  The  movable  slide  carrying  the  clip  K  is 
then  adjusted,  until  the  edge  of  the  clip  just  touches  the  right 
hand  end  of  the  diagram,  the  presure  of  the  clips  upon  the 
paper  serving  to  secure  it  firmly  while  the  work  upon  it  is  be- 
ing performed.  The  slide  to  which  the  clip  K  is  secured,  is 
fitted  so  that  only  a  slight  pressure  of  the  thumb  or  finger  is 
required  to  move  it  in  either  direction. 

The  mean  effective  pressure  of  an  indicator  diagram  being 
one  of  the  principal  factors  in  the  computation  of  power  of 
steam  engines,  hence  this  particular  location  of  the  diagram 
upon  the  board  (as  represented  in  the  cut)  is  only  necessary 
where  the  finding  of  this  quantity  is  desired.  Otherwise,  in 
cases  where  only  the  area  of  the  diagram  or  other  irregular 
figure  is  needed,  it  may  be  placed  in  any  desired  position  with- 
out reference  to  any  point,  and  the  area  read  directly  from  the 
graduated  wheel.  The  instrument  is  then  arranged  upon  the 
board  with  its  guide  pin  inserted  in  the  groove  of  the  guide  I, 
and  secured  therein  by  the  weight  Q.  The  tracing  point  O  is 
then  moved  to  the  extreme  right  hand  end  of  the  diagram, 
where  the  line  is  in  contact  with  the  clip  K  (as  shown  at  D). 
Here  make  a  slight  indentation  in  the  paper,  by  pressing  the 
thumb  against  the  top  of  the  tracing  point ;  this  gives  the  start- 
ing point  from  which  to  trace  around  the  diagram 

The  zero  mark  of  the  graduated  wheel  is  then  turned  and 
made  to  exactly  coincide  with  the  zero  mark  on  the  vernier. 
In  commencing  operations  the  direction  in  which  the  diagram 
should  be  followed  by  the  tracing  point  is ;  first  along  the  back 


A  nd  Its  Appliances.  1 89 

pressure  and  compression  lines,  thence  returning  by  way  of  the 
expansion  curve  to  the  starting  point.  The  only  object  in 
tracing  in  this  direction  being  that  the  main  divisions  on  the 
wheel  are  numbered  towards  the  left  from  the  zero  mark,  and 
consequently  in  this  direction  any  movement  of  the  wheel  is 
recorded  in  regular  order,  as  1,2,  3,  etc.,  whereas,  if  the  diagram 
is  traced  in  the  opposite  direction,  the  reading  will  be  the  re- 
verse of  this,  as  14,  13,  12,  etc.,  and,  although  the  circumfer- 
ential movement  of  the  wheel  would  be  precisely  the  same  in 
either  case,  the  only  consequence  of  tracing  the  diagram  in  the 
latter  direction  would  be  the  inconvenience  of  reading  the 
areas. 

In  the  measurement  of  indicator  diagrams,  for  mean  effec- 
tive pressure,  no  attention  whatever  need  be  given  to  reading 
the  areas.  After  the  tracing  point  has  made  a  complete  circuit 
and  again  reached  the  starting  point,  it  is  then  moved  upward 
along  the  edge  of  the  clip  K  until  the  zero  mark  of  both  the 
wheel  and  vernier  coincide.  Another  slight  indentation  is 
then  made  at  this  point,  (as  shown  in  the  cut  at  A).  The  dis- 
tance between  these  two  indentations  (D  and  A)  represents  the 
average  height  of  the  card,  and  also,  if  this  is  measured  with  a 
scale  corresponding  in  pounds  to  the  denomination  of  the 
spring  with  which  the  diagram  was  taken  the  said  measure- 
ment will  be  the  mean  effective  pressure  of  the  diagram  in 
pounds  per  square  inch,  according  to  the  spring  and  scale  used. 

Where  two  diagrams  are  taken  on  the  same  card  it  is  ad- 
visable to  measure  and  find  the  average  pressure  separately ; 
for  the  purpose  of  comparison  with  each  other.  By  the  use  of 
this  instrument  all  imperfections  or  irregularities  whatever  in 
the  outline  of  the  diagrams  whether  to  be  added  or  subtracted, 
are  accounted  for,  and  the  final  results  given  exact.  For  in- 
stance, where  a  loop  is  formed  in  the  diagram  (as  in  Fig.  62) 
caused  by  the  expansion  line  crossing  the  atmospheric  line 
early  in  the  stroke ,  and  running  below  to  the  end,  thereby 


19°  Steam  Engine  Indicator 

dividing  the  diagram  into  two  distinct  parts,  its  outline  should 
be  traced  in  the  same  manner  as  is  done  in  any  well  formed 
diagram,  as  the  principle  upon  which  the  instrument  is  con- 
structed, enables  it  to  perform  the  operation  of  addition  or  sub- 
traction with  the  greatest  exactness  and  will  consequently  sub- 
tract the  effect  of  the  said  loop  from  the  positive  part  of  the 
diagram  and  the  reading  of  the  instrument  after  the  diagram 
has  been  traced,  will  give  the  net  average  pressure  per  square 
inch  throughout  the  stroke. 

Where  the  instrument  is  used  to  measure  the  area  of  any 
figure,  it  is  only  necessary  to  select  a  starting  point.  Adjust 
the  zero  marks  on  the  wheel  and  vernier  to  coincide,  and  trace 
around  the  outline  of  the  figure,  then  its  correct  area  will  be 
found  from  an  observation  of  the  number  of  main  divisions, 
and  subdivisions  of  the  wheel  that  have  passed  beyond  the 
zero  mark  on  the  vernier. 

For  example :  Suppose  upon  noting  the  number  of  main 
divisions  of  the  wheel  that  have  passed  the  zero  mark  of  the 
vernier,  we  find  the  largest  figure  to  be  three  (3)  which  will 
represent  inches,  and  the  number  of  sub-divisions  that  have 
also  passed  the  zero  mark  of  the  vernier,  to  be  four  (4),  each 
subdivision  representing  one-fifth  (1-5)  or  twenty-hundredths 
(.20)  of  a  square  inch,  and  the  number  of  the  division  on  the 
verneir  which  exactly  coincides  with  a  division  on  the  wheel  to 
be  two  (2),  each  representing  two-hundredths  (.02)  of  a  square 
inch,  therefore  the  reading  taken  from  the  instrument  in  this 
position  will  be  3+(4X  .2o)+(2X  .02)=  3. 84  square  inches,  as  the 
area  of  figure.  This  instrument  being  of  careful  and  delicate 
construction,  should  be  handled  with  the  greatest  care  and 
kept  perfectly  free  from  any  matter  that  might  interfere  with 
the  movement  of  the  wheel ;  thereby  insuring  accurate  results. 

To  a  great  many  users  of  the  Averager  or  Planimeter, 
shown  and  described  in  Fig.  87,  it  may  be  considered  a  fact 
that  the  reason  and  principle  upon  which  its  accuracy  is  based, 


And  Its  Appliances.  191 

in  the  measurement  of  the  area  of  any  irregular  figure,  is,  to  a 
certain  extent,  shrouded  in  mystery;  but  nevertheless  it  is 
well-known  that  a  comparison  of  its  readings,  taken  from 
figures  of  known  areas,  prove  its  reliability  and  correctness, 
and  can  under  all  circumstances  be  depended  upon  for  correct 
results ;  hence,  a  study  of  the  theory  of  its  operation  may  be 
interesting  to  many. 

The  manipulation  of  the  instrument  being  easily  per- 
formed, as  before  described,  and  its  theory  quite  simple,  we 
shall  endeavor  to  make  clear  and  explain  why,  by  simply 
passing  the  tracing  point  around  the  outline  of  a  given  figure, 
its  exact  area  will  be  denoted  on  the  registering  wheel.  In 
attempting  this  we  shall  leave  out,  wherever  possible,  the  use 
of  the  higher  mathematics^  usually  employed  in  connection 
with  a  discussion  of  the  subject,  and  also  shall  first  consider 
the  instrument  in  its  application  to  the  measurement  of  areas, 
and  which  consideration  will  also  apply  in  principle  to  all  other 
planimeters.  Although  the  principle  is  simple,  still  it  is 
necessary  for  the  reader  not  conversant  with  it,  to  follow 
closely  the  explanation  in  order  to  become  familiar  with  the 
peculiar  movements  and  actions  of  the  registering  wheel. 

In  Fig.  88  the  outline  A,  Ai,  C,  D  and  A3,  is  assumed 
for  our  purpose  to  represent  an  indicator  diagram,  the  expan- 
sion curve  being  shown  in  dotted  lines.  The  point  "A  on  the 
diagram  is  selected  as  the  starting  point  from  which  to  trace 
and  consider  the  figure.  Probably  a  better  idea  may  be  had, 
by  first  confining  our  study  of  the  subject  to  a  part  of  the 
diagram ;  that  is,  the  area  of  the  square  inclosed  by  the  lines 
A,  Ai,  A2  and  A3.  The  line  Ai-Bi  represents  the  arm  of  the 
instrument,  and  shows  its  position  after  the  tracing  poirit  has 
been  moved  horizontally  away  from  the  starting  point  A  to  the 
position  at  Ai.  This  line  (Ai-Bi)  may  be  assumed  to  be  a 
small  round  rod,  the  end  (Bi)  being  guided  to  always  move  in 
a  straight  line,  as  shown  by  dotted  line  from  Bi  to  63 ;  while 


192  Steam  Engine  Indicator 

the  end  (Ai)  carrying  the  tracing  point  is  free  to  be  moved  in 
any  direction,  and  to  any  point  of  the  diagram.  This  arm  or 
rod  is  also  shown  here  as  the  axis  of  the  registering  wheel  W, 
and  is  represented  in  this  way  for  the  purpose  of  simplifying 
matters  in  the  way  of  its  demonstration,  and  because  the  final 
results  of  the  registering  wheel  W,  in  having  its  axis  coincident 
with  the  arm  Ai-Bi,  will  be  precisely  the  same  as  though  its 
axis  was  located -at  a  distance  from,  and  parallel  to,  a  line 
drawn  between  the  tracing  point  Ai  and  guide  pin  at  Bi  ; 
(this  latter  construction  being  that  of  the  instrument  repre- 
sented in  Fig.  87).  In  the  diagram  the  four  positions  of  the 
registering  wheel  are  shown  at  Wo,  W,  Wi  and  W2,  when  the 
tracing  point  is  respectively  at  each  corner  of  the  square  or 
rectangle  A,  Ai,  A2  and  AS. 

Suppose  the  tracer  to  be  at  the  starting  point  A — the  arm 
then  coinciding  with  line  A-B,  and  the  registering  wheel  at 
Wo ;  now,  any  movement  at  the  tracing  point  up  or  down  on 
that  line  will  simply  cause  the  wheel  to  slide  in  the  same 
direction,  but  without  causing  any  rotation  of  it,  because  its 
axis  is  coincident  or  parallel  to  said  line ;  hence,  any  move- 
ment of  the  wheel  in  a  direction  parallel  to  its  axis  will  not 
cause  rotation. 

If,  now,  the  tracing  point  be  moved  to  the  right,  in  a  hori- 
zontal direction,  until  the  arm  is  in  the  position  Ai-Bi,  then 
the  wheel  has  moved  from  Wo  to  W,  and  has  revolved  a 
certain  distance  at  its  periphery ;  the  amount  depending  upon 
the  degree  of  the  angle  formed  by  its  departure  from  the 
starting  point,  or  line  A-B ;  but,  any  consideration  of  the  amount 
of  this  movement,  as  a  factor  in  the  case,  is  wholly  unnecessary, 
because  all  motion  imparted  to  the  wheel  by  its  departure  from 
the  line  A-B  is  always  exactly  cancelled  (in  whatever  direction 
it  may  return)  on  arriving  at  the  starting  point. 

Now,  consider  the  action  of  the  wheel  in  an  assumed  down- 
ward  movement  of  the  arm,  from  its  position  Ai-Bi  to  a 


And  Its  Appliances. 


193 


position  A2-B2,  then  the  area  swept  over  by  the  arm  is  the 

space  Ai-Bi,  A2-B2, 
which  is  exactly  equal 
in  area  to  that  [of  the 
square,  or  rectangle  A, 
A  i ,  A2  and  A3 ,  because 
they  both   have    the 
same  base,  and  between 
the  same   parallels. 
The  result  of  this  move- 
ment of  the  arm  will  cause  the  register- 
ing wheel  to  move  from  W  along  the 
dotted  line  to  the  position  Wi.     The 
wheel  being  in  contact  with  the  paper, 
and  the  direction  of  its  movement  from 
W  to  W  i,  at  an  angle  with  its  axis,  will 
consequently  cause  it  to  revolve  while  being 
moved  downward  to  Wi,  and  the  amount 
of  this  motion  at  its  periphery  will  be  re- 
presented by  the  line  W-N,  which  is  the  sine 
of  the  angle  W,  Wi,  N,  with  Wi-W  as  the 
radius  of  the  circle  ;  consequently,  by  knowing 
this  angle,  the  length  of  its  sine  can  be  found 
from  a  table  of  sines,  in  which  their  lengths 
are  given    for   any   angle,    the   radius  being 
unity.    Suppose,  for  example,  the  angle  formed 
between  the  arm  A2-B2,  and  the  vertical  line 
of  movement  of  the  wheel  from  W  to  W  i ,  to 
be  one  of   18^  degrees,  and  that  the  vertical 
distance  traversed  by  the  wheel  to  be  two  (2) 
inches ;  then  from  a  table  we  find  the  sine  for 
that  angle  to  be  .  32  in  terms  of  inches,  at  unity. 
Therefore,  if  this  be  multiplied  by  the  verti- 
cal movement,  two  (2)  inches  (. 32  X  2  =  .64  in.), 
this  product  will  be  the  length  of  the  line  W-N. 


#O 


FIG.  88. 


194  Steam  Engine  Indicator 

The  rotary  motion,  therefore,  that  has  been  imparted  to 
the  periphery  of  the  wheel  (by  being-  in  contact  with  the  paper 
over  which  it  runs),  in  moving  from  W  to  Wi,  is  equal  to  the 
length  of  the  line  W-N,  and  the  final  result  in  the  readings  are 
precisely  the  same  as  though  the  wheel  was  first  rolled  in  the 
direction  of  its  rotation  upon  the  line  W-N,  and  then  without 
rolling  moved  down  the  line  A2-B2,  coincident  with  its  axis  to 
Wi ;  hence,  this  distance  (W-N)  if  multiplied  by  the  length  of 
the  arm  Ai-Bi  (W-Nx  Ai-Bi),  is  equal  to  the  area  of  the  space 
passed  over  by  the  arm,  and  is  also  equal  to  the  square  or 
rectangle  A,  Ai,  A2  and  A3,  for  the  reason  before  stated,  both 
having  the  same  base,  and  between  the  same  parallels. 

Suppose  now  the  tracing  point  to  be  moved  from  its  posi- 
tion A2  to  A3  ;  in  doing  this  the  wheel  will  have  moved  from 
its  position  Wi  to  W2,  and  revolved  at  its  periphery  an  amount 
exactly  equal  to  that  which  it  revolved  in  being  moved  from 
A  to  Ai.  Therefore,  as  the  wheel  has  revolved  through  the 
same  angle  in  both  cases,  but  the  motion  being  in  opposite 
directions,  will  thereby  cancel  each  other,  and,  as  a  conse- 
quence, leave  no  positive  results  on  the  registering  wheel. 

In  moving  upward  from  A3  to  the  starting  point  at  A,  the 
wheel  will  not  revolve,  because  this  movement  is  parallel  to 
its  axis. 

From  a  careful  consideration  and  study  of  the  matter,  the 
following  facts  may  be  deducted  and  readily  observed: — ist. 
That  all  movements  of  the  tracing  point  that  are  in  a  direction 
parallel  to  the  axis  of  the  wheel,  will  not  cause  it  any  revolu- 
tion. 2d.  That  all  revolution  of  the  wheel  caused  by  a  de- 
parture of  the  tracer  from  the  starting  point  A,  will  be  exactly 
cancelled  on  its  return  to  that  point.  3.  That  the  only  perma- 
nent record  remaining  on  the  wheel  (after  tracing  the  diagram), 
is  derived  entirely  from  vertical  movements  of  the  tracer  rela- 
tive to  the  starting  point  A,  the  amount  of  its  revolution 
depending  upon  the  angle  formed  by  the  .arm  with  the  line 


And  Its  Appliances.  195 

A-B,  together  with  the  vertical  distance  passed  over  by  the 
tracer.  4th.  That  the  amount  of  revolution  of  the  wheel  is 
always  equal  to  the  sine  of  the  angle  (formed  by  its  axis  with 
the  direction  of  its  movement),  multiplied  by  the  distance  of 
its  vertical  movement.  It  also  becomes  evident  that  any 
departure  of  the  tracer  Ai  from  the  starting  point  A,  is  pro- 
portional to  the  sine  of  the  angle  so  formed,  multiplied  by 
the  length  of  the  arm  Ai-Bi.  Supposing  this  angle  to  be  one 
of  187^  degrees  (the  same  as  the  previous  example),  the  sin  3 
of  which  at  unity  is  .32  inches,  and  the  length  of  the  arm 
Ai-Bi  to  be  6. 25  inches,  then  (.32x6.25  =  2  inches),  the  dis- 
tance of  the  tracer's  departure  from  A.  This  product,  then, 
if  multiplied  by  any  vertical  movement  of  the  tracer,  is  equal 
to  the  area  corresponding  to  such  movement. 

If  in  place  of  moving  the  tracer  to  Ai  it  had  been  stopped 
at  the  point  4,  and  moved  down  the  line  to  5,  and  thence 
through  A3  to  the  starting  point  A,  the  area  of  this  rectangle 
recorded  on  the  wheel  would  be  just  one-half  that  of  A,  Ai, 
A2  and  A3,  because  this  angle  is  proportionately  one-half  of 
the  former,  thereby  making  it  more  acute,  and  consequently 
its  sine  would  also  be  only  one-half.  The  effective  rotary  mo- 
tion of  the  wheel  in  this  case  is  derived  entirely  from  its  verti- 
cal movement  along  the  line  from  4  to  5.  Therefore  by  apply- 
ing the  rule  (Ai.Bi  X  sine  of  angle  X  vertical  movement  = 
area),  it  will  be  found  that  the  area  of  the  latter  is  only  one- 
half  that  of  the  larger  rectangle. 

We  may  now  consider  the  whole  of  the  diagram.  Fig.  88, 
including  the  dotted  curve  line  Ai,  C. ;  and  in  doing  so  it  must 
be  understood  that  whatever  has  been  said  in  reference  to  the 
larger  rectangles,  is  equally  true  of  any,  and  all,  others  that 
may  be  inscribed  within  its  extreme  outline ;  (however  numer- 
ous, whatever  their  size,  and  wherever  located).  If  in  addi- 
tion to  the  larger  rectangles  we  inscribe  smaller  ones,  num- 
bered 1.2,  and  3  in  the  diagram,  and  from  the  starting  point 


196  Steam  Engine  Indicator 

A,  carry  the  tracer  around  their  extreme  outline,  so  as  to  in-- 
elude  their  measurements;  it  will  be  found  on  returning  to  the 
starting  point,  that  the  reading  on  the  wheel  will  be  increased 
by  an  amount  just  equal  to  the  combined  areas  of  the  smaller 
rectangles  1-2  and  3,  (over  the  readings  taken  from  the  larger 
ones  contained  in  the  square  A-Ai-A2  arid  A3  :)  and  such  read- 
ing will  be  approximately  the  area  of  the  diagram. 

Other  additional  smaller  rectangles  may  still  be  inscribed 
in  the  spaces  adjacent  to  the  dotted  curved  line ;  (said  space 
yet  remaining  unaccounted  for  in  the  reading;)  And  if  these 
smaller  rectangles  should  be  made  sufficiently  numerous,  and 
measured  separately,  by  passing  the  tracer,  in  turn,  around 
the  extreme  outline  of  each,  without  removing  from  the  paper, 
the  wheel  would  mechanically  add  the  area  of  these  rectangles 
together,  and  on  the  return  of  the  tracer  to  the  starting  point 
A,  the  reading  of  their  combined  sum  would  be  exactly  equal 
to  the  area  of  the  whole  diagram  ;  and  which  will  also  be  equiv- 
alent to  the  reading  that  would  appear  on  the  wheel  after  pass- 
ing the  tracer  around  the  outline  of  the  diagram,  including  the 
curved  line  Ai,  C. 

Therefore  it  will  be  seen  that  as  the  horizontal  movements 
of  the  tracer,  over  the  lines  of  any  rectangle,  cancel  each  other, 
while  only  vertical  movements  relative  to  the  starting  point  A, 
leave  any  permanent  record  on  the  wheel,  the  results  will  be 
precisely  the  same  as  though  the  tracer  had  simply  moved  over 
the  actual  extreme  outline  of  the  diagram 

As  the  area  of  any  rectangle  or  parallelogram,  is  equal  to 
the  product  of  its  length  multiplied  by  its  vertical  height,  it  is 
readily  seen,  that  after  passing  the  tracer  once  around  the  out- 
line of  any  figure,  (regular  or  irregular;)  its  exact  area  will  be 
denoted  by  the  number  of  divisions  of  the  wheel  that  have 
passed  the  zero  mark  on  the  vernier ;  consequently  the  neces- 
sary height  of  a  rectangle  of  the  same  length,  to  contain  the 
same  area  may  be  determined  by  moving  the  tracer  upward  along 
the  clip  K.  until  the  same  number  of  divisions  have  returned ; 
and  the  zero  marks  on  the  wheel,  and  vernier  again  coincide, 


A  nd  Its  Appliances.  1 97 

(as  mentioned  in  the  description  of  the  instrument  in  Fig.  87), 
which  point  will  be  the  average  height  of  a  parallelogram,  con- 
taining exactly  the  same  area  as  the  figure  traced.  Therefore 
in  case  the  figure  traced  be  an  indicator '( diagram,  such  point 
must  be  its  average  height,  because  it  is  the  height  of  a  rec- 
tangle of  the  same  length,  and  same  area  as  the  diagram.  Con- 
sequently if  this  average  height  be  measured  by  the  scale  of 
the  spring  with  which  the  diagram  was  taken,  the  units  of  the 
scale  will  show  the  mean  effective  pressure  in  pounds  per  square 
inch  throughout  the  stroke  of  the  engine  without  any  compu- 
tation whatever. 

The  number  of  parts  into  which  the  circumference  of  the 
wheel  may  be  divided;  can  be  10-15-20  or  any  other  convenient 
number ;  the  only  requisite  being,  that  the  circumference  of 
the  registering  wheel  shall  be  so  proportioned  that  one  com- 
plete revolution  on  its  axis,  would  cause  it  to  roll  over  the 
paper  an  amount,  such,  that  if  this  distance  was  multiplied  by 
the  length  of  the  tracer  arm,  that  their  product  will  be  equal  to 
the  area  of  a  rectangle  containing  exactly  some  whole  number  of 
square  inches;  (suppose  for  example  fifteen;)  now  if  the  cir- 
cumference of  the  wheel  be  graduated  into  the  same  number 
of  divisions,  and  numbered  accordingly  from  one  to  fifteen, 
then  each  division  on  the  wheel  will  represent  one  square 
inch ;  and  the  area  of  any  figure,  after  the  tracing  point  has 
passed  around  its  outline,  will  be  indicated  in  square  inches, 
according  to  the  number  of  divisions  of  the  wheel  that  have 
passed  a  given  point.  We  again  mention  the  necessity  of 
handling  the  instrument  with  great  care  in  order  to  obtain  the 
most  accurate  results ,  never  allowing  the  contact  edge  of  the 
registering  wheel  to  become  indented  in  the  least,  keep  perfect- 
ly free  from  rust  or  deposit  of  any  kind,  and  a  good  plan,  is  to 
pass  a  thin  piece  of  paper  between  the  wheel  and  vernier  to 
remove  any  particles  of  dust  that  may  accumulate  and  destroy 
the  free  action  of  the  wheel ;  see  that  the  spindle  runs  easily, 
and  freely  between  the  centres,  and  practically  without  end 
play ;  and  care  must  also  be  taken  to  prevent  the  tracer  arm 
from- getting  bent  or  in  any  way  out  of  shape. 


198 


Steam  Engine  Indicator 


The  Amsler  Polar  Planimeter.  Illustrated  in  Fig.  89 
is  another  device  for  measuring  diagrams:  This  instru- 
ment does  not  give  the  mean  effective  pressure  directly, 
but  it  determines  the  area  of  the  diagram,  and  from 
this  area  the  mean  effective  pressure  is  computed  in 

the  manner  described.  It  con- 
sists of  the  two  arms,  A  and 
D,  and  the  measuring  wheel, 
C.  To  operate  it,  a  piece  of 
smooth,  hard  paper  is  laid  on 
the  table,  and  the  instrument 
placed  upon  it,  with  the  needle 
point,  A,  pressed  into  the  board. 
This  point  serves  as  a  centre 
about  which  the  apparatus  is 


Fie.  8t). 

turned.  The  indicator  card  is  laid  under  the  tracer, 
B,  and  held  either  by  tacks,  which  fasten  it  to  the 
table,  or  what  is  quite  sufficient,  by  the  pressure  of 
the  fingers.  The  tracing  point  is  set  on  the  line  of 
the  diagram — say  near  the  middle  of  the  steam  line — and  a 
slight  indentation  made  in  the  paper,  to  serve  as  a  starting 


A  nd  Its  Appliances.  1 99 

point.  The  graduated  wheel  is  set  at  the  zero  mark.  The 
tracer  is  then  moved  over  the  line  of  the  diagram  in  the  di- 
rection of  motion  of  the  hands  of  a  watch,  finally  making  a 
complete  circuit,  and  returning  to  the  starting  mark.  The 
number  of  divisions  and  fractions  of  a  division  shown  on 
the  wheel  at  the  point  opposite  the  stationary  zero  mark,  indi- 
cates the  area  of  the  diagram  traced.  The  wheel  has  ten  main 
graduations,  each  of  which  represents  one  square  inch  of  area. 
Each  main  division  is  subdivided  ten  times,  and  each  subdi- 
vision represents  one-tenth  of  a  square  inch  of  area.  A 
stationary  vernier  scale  E  is  placed  beside  the  graduated  edge  of 
the  wheel,  and  serves  to  indicate  the  smaller  fractions,  viz., 
hundredths.  To  read  the  vernier,  the  eye  is  run  along  the 
stationary  scale  till  a  line  of  division  is  found  which  is  just 
opposite  a  division  on  the  wheel.  The  number  of  the  division 
on  the  vernier,  reckoned  from  the  zero  mark,  is  the  number  of 
hundredths  sought.  If,  for  example,  the  reading  of  the  area 
is  two  main  divisions  on  the  wheel,  and  four  of  the  subdivisions 
and  the  line  of  coincidence  on  the  vernier  is  number  seven 
reckoned  from  zero,  the  area  sought  is  2.47  sq.  in. 

To  reduce  this  to  mean  effective  pressure,  two  perpen- 
dicular lines  are  drawn,  one  through  each  terminal  point  of 
the  diagram,  and  the  length  of  the  diagram  is  measured  by 
measuring  the  distance  between  these  two  perpendiculars. 
Suppose  this  distance  is  3.78  in.,  and  suppose  the  number  of 
the  spring  employed  is  No.  40.  Then  the  mean  effective  pres, 
sure  is  found  by  dividing  40  by  3.78  and  multiplying  the  result 
by  2.47.  Making  this  computation  the  mean  effective  pressure 
sought  is  26. 13  Ibs.  per  sq.  in. 

In  working  the  Polar  Planimeter,  care  must  be  observed 
to  place  the  diagram  so  that  the  two  arms  are  not  brought  too 
near  each  other  at  one  end  of  the  course,  nor  yet  carried  too 
far  apart  at  the  other  end.  At  a  point  midway  between  the 
two  extremes  the  two  arms  should  lie  about  perpendicular  to 
each  other. 


2OO  Steam  Engine  Indicator 

As  an  example  of  the  manner  of  computing  the  horse- 
power of  an  engine,  suppose  an  engine  has  a  cylinder  1 5  inches 
in  diameter,  a  piston  rod  2  y2  inches  in  diameter,  a  stroke  of 
2^  feet,  running  at  a  speed  of  135  revolutions  per  minute. 
Suppose  the  indicator  diagrams  show  a  mean  effective  pressure 
of  36  Ibs.  per  square  inch,  this  being  the  average  of  the  indi- 
cations at  the  two  ends.  The  area  of  the  cylinder  to  be  used 
is  the  net  area  obtained  by  deducting  one-half  the  area  of  the 
rod.  The  area  of  a  cylinder  15  inch  in  diameter  is  176.71 
square  inches. 

One-half  the  area  of  a  rod  2J^  inches  in  diameter  2.45 
square  inches.  The  net  area  to  be  used  in  the  computation  is 
176.71  —  2.45=174.26  square  inches.  The  speed  in  feet  per 
minute  is  135X2^X2  =  675  feet.  The  horse-power  developed, 
therefore,  is 

36x174.26x675^      4,234,518^      I2g      H    p 
33,000  33.000 

That  is 
M.E.P.  X  net  area  of  cyl.  insq.  ins.  X  piston  speed  in  ft.  per  min. 

33.000 

When  the  engine  has  more  than  one  cylinder,  the  power  de- 
veloped in  each  cylinder  is  computed  in  the  manner  given,  and 
the  results  added  together. 


And  Its  Appliances. 


201 


CHAPTER    XXIV. 


COMPARISON    OF   DIAGRAMS    FROM    THROTTLING   AND 
CUT-OFF    ENGINES. 


The  following  diagrams  in  this  chapter  were  taken  from 
what  originally  was,  (when  new)  a  pair  of  side  by  side  non- 


FIG.  91. 

condensing  throttling  engines,    and  connected   to  the  crank 
shaft  at  right  angles,  or  quartering. 


2O2 


Steam  Engine  Indicator 


After  running  in  this  manner  for  some  time  it  was  deemed 
advisable,  and  also  as  an  experiment,  to  convert  the  valve 
motion  of  one  of  the  pair  into  a  special  automatic  cut-off  valve 
gear  in  order  to  use  the  steam  expansively  on  one  engine,  and 
throttling  on  the  other. 

This  alteration  of  the  engine  being  completed,  the  dia- 
grams both  in  Fig.  90  and  Fig.  91  in  connection,  were  taken 
to  show  the  extreme  range  of  this  new  valve  gear. 


FIG.   92. 


FIG.    93. 

The  diagrams  from  Fig.  92  to  Fig.  103  inclusive,  are  fac- 
similas  of  diagrams  taken  in  pairs,  after  this  alteration  had 
been  made  on  the  engine ;  having  one  cylinder  throttling,  and 
the  other  with  automatic  valve  gear,  and  were  taken  to  illus- 
trate the  difference  in  the  two  systems  of  government  at  diff- 
erent loads ;  the  data  of  the  engine  being  as  follows : 


And  Its  Appliances. 


203 


AUTOMATIC  ENGINE 

Dia.  of  Cylinder,          i5T3g-  in. 
"•>      "  Piston  Rod,      2^3   " 
Length  of  Stroke,       42        " 
Revolutions  per  min.          60 
Piston  speed  "     "  420' 


THROTTLING  ENGINE 

Dia.  of  Cylinder,         15^/3  in. 
"      "  Piston  Rod,      25/3   " 
Length  of  Stroke,       42       " 
Revolutions  per  min.          60 
Piston  speed  "       "  420' 

Scale  of  Spring,  40 


Scale  of  Spring,  40 

Thus  giving  a  value  of  the  engine  constant  on  the  auto- 
matic side  of  2.275,  and  of  the  throttling  side  2.334,  indicated 
horse  power,  for  each  pound  of  mean  effective  pressure,  at  a 
speed  of  60  revolutions  per  minute. 


FIG.   94. 


FIG.   95. 

In  calculating  the  horse  power  from  the  diagrams,  the 
factor  that  has  been  used  to  represent  speed  has  been  the 
actual  number  of  revolutions  of  the  engine,  at  the  time  each 
diagram  was  taken. 


204 


Steam  Engine   Indicator 


The  mean  effective  pressure  was  obtained  by  the  use  of  a 
planimeter,  and  the  steam  or  water  consumption,   computed 

by  the  formula 


A  T  pM  E  P  that  is'  by  dividin£  the 
constant  859375,  by  the  volume  of  the  steam  at  absolute  term- 
inal pressure,  multiplied  by  the  mean  effective  pressure  in 
pounds  per  square  inch  of  the  diagram ;  the  quotient  being  the 
number  of  pounds  of  steam  or  water  consumed  per  hour  per 
each  indicated  horse  power  developed  by  the  engine. 


FIG.  96. 


FIG.   97. 

In  the  latter  calculation  however,  no  allowance  has  been 
made  for  compression  and  clearance ;  the  rule  for  making  such 
allowance  being  described  in  connection  with  Fig.  77,  Chapter 
XXI 

These  diagrams  were  selected  from  a  large  number,  with 
two  objects  in  view ;  first  to  show  the  different  forms  or  outlines 
of  the  pressure  areas  between  the  automatic,  and  throttling 


And  Its  Appliances. 


205 


system  of  governing,  from  pairs  of  diagrams  of  approximately 
the  same  horse  power  ;  and  second,  to  show  the  relative  rates  of 
water  or  steam  consumption  of  each,  in  pounds  per  horse 
power  per  hour. 

In  addition  the   diagrams   from   the    automatic  side   also 
show  that  the  minimum  amount   of  steam  consumption   (and 


FIG.   98. 


FIG.   99. 

consequently  the  greatest  economy)  occurs  in  diagrams  No.  5, 
Figs.  100  and  101,  where  the  cut-off  takes  place  at  about 
twenty-two  hundredths  of  the  stroke,  corresponding  to  about 
4.57  ratio  of  expansion,  and  to  very  nearly  the  generally  con- 
sidered most  economical  point  of  cut-off  in  automatic  engines 
working  at  a  steam  pressure  of  from  60  to  75  pounds  pressure 
per  square  inch. 


206 


Steam  Engine   Indicator 


By  reference  to  the  diagrams  from  either  the  automatic 
or  throttling  engine  it  will  be  observed  that  a  gradual  decrease 
in  the  water  consumption  takes  place  as  the  power  developed 
by  the  engine  increases,  or,  as  in  case  of  the  automatic  engine, 
when  the  .cut-off  takes  place  later  in  the  stroke. 

The  minimum  consumption  appears  to  have  been  reached 


FIG.    100. 


FIG.   101. 

in  either  case,  in  the  diagrams  Nos.  5 ,  and  it  will  be  seen  that 
in  all  diagrams  on  either  side  whether  developing  more  or  less 
power,  that  an  increase  in  the  rate  of  water  consumption  in- 
varibly  takes  place. 

In  these  diagrams  the  economy  of  the  automatic  cut-off 
engine,  over  that  of  the  ordinary  throttling  system  is  very 


And  Its  Appliances. 


207 


fairly  exhibited,  and  shows  the  relative  economy  that  might 
be  expected  from  the  automatic,  under  ordinary  circumstances, 
over  that  of  the  throttling  system  of  regulation. 

The  outlines  of  the  various  diagrams  of  each  system  ar.e 
fair  representations  of  what  ought  to  be  expected  from  an  en- 
gine with  properly  designed  valve  gear,  and  with  evenly  and 
accurate  adjustments  of  the  same. 


FIG.   102. 


FIG.   103. 

It  must  be  understood  that  the  diagrams  here  presented 
are  not  intended,  or  claimed,  as  representing  the  highest  effi- 
ciency and  economy  obtainable,  but  are  only  given  from  actual 
ordinary  practice,  in  order  to  be  able  to  make  an  interesting 
comparison  between  the  two  systems  of  regulation. 


2O8  Steam  Engine    Indicator 


CHAPTER  XXV. 


ECONOMY    OF    EXPANSION. 


As  regards  the  economy  of  expansion  it  will  be  found  by 
reference  to  the  Table  No.  8  on  the  properties  of  saturated 
steam  that  the  weight  of  a  given  volume  of  steam  varies  very 
nearly  in  proportion  to  its  pressure  that  is,  a  cubic  foot  of  steam 
at  60  pounds  pressure  weighs  approximately  twice  as  much  as 
the  same  volume  at  30  pounds  pressure. 

A  given  weight  of  steam  represents  the  same  weight  of 
water  that  must  be  evaporated  to  produce  it,  consequently  the 
lower  the  terminal  pressure  at  the  end  of  the  stroke  in  a  given 
cylinder  the  less  will  be  the  amount  of  water  exhausted  as 
steam ;  and  as  the  measure  of  the  work  done  in  the  cylinder  by 
the  steam,  is  proportional  to  the  mean  effective  pressure,  it 
becomes  evident  that  economy  in  the  use  of  steam  in  an  en- 
gine, consists  in  getting  a  high  mean  effective  pressure,  in 
connection  with  a  low  terminal  pressure. 

This  can  only  be  accomplished  by  cutting  off  the  supply  of 
steam,  at  a  time  when  the  piston  has  only  completed  a  part  of 
its  stroke,  and  by  that  means  obtain  an  additional  amount  of 
work  from  the  expanding  steam  to  the  end  of  the  stroke. 

Suppose  in  a  steam  cylinder  using  steam  at  100  pounds  ab- 
solute, the  steam  be  cut  off  when  the  piston  has  moved  one- 
fourth  of  its  stroke,  then  the  mean  pressure  calculated  accord- 
ing to  the  rule  in  Chapter  1 8  will  be  almost  60  pounds ;  and 


And  Its  Appliances.  209 

this  is  obtained  by  using  only  one-quarter  of  a  cylinder  full  of 
steam ;  whereas  if  the  entire  cylinder  had  been  filled  the  mean 
pressure  would  have  been  only  100  pounds,  with  an  expendi- 
ture of  four  times  the  quantity  of  steam  used  as  when  cutting 
off  at  one-quarter  stroke. 

This  indicates  the  direction  in  which  a  saving  is  effected ; 
but  in  practice  however,  condensation  in  the  cylinder,  and 
other  causes  prevent  this  full  theoretical  gain  from  expansion 
being  realized ;  at  the  same  time  however  the  gain  from  this 
source  is  an  important  one. 

Therefore  from  what  has  been  said  in  this  connection  it 
would  be  natural  to  expect,  in  considering  diagrams  from  first- 
class  cut-off  engines,  to  find  the  initial  pressure  of  the  diagram 
high,  as  compared  with  the  boiler  pressure,  also  with  straight 
or  fairly  straight  steam  lines,  and  sharp  cut-off ;  because  these  all 
tend  to  bring  about  both  high  mean  effective,  and  low  terminal 
pressure ;  also  whatever  tends  to  make  the  terminal  pressure 
higher  than  it  should  be,  represents  waste  of  steam. 

Economy  of  High  Pressure.  It  is  a  well  established  fact  that 
the  use  of  steam  of  a  high  pressure  tends  to  greater  economy 
in  the  engine ;  the  reason  for  which  is  simply  as  follows : 

Suppose  in  this  case  an  engine  working  without  expansion, 
and  in  order  to  simplify  the  matter,  assume  that  there  is  no 
clearance.  Assume  also  the  engine  to  be  working  non-con- 
densing, with  an  absolute  back  pressure  of  1 5  pounds,  or  three- 
tenths  above  the  atmosphere. 

If  steam  of  20  pounds  absolute  pressure  is  used  in  the  cyl- 
inder, the  mean  effective  pressure  on  the  piston  is  20—15  =  5 
pounds. 

If  the  piston  has  a  total  displacement  of  one  cubic  foot, 
then  we  are  using  one  cubic  foot  of  steam,  of  a  pressure  of  20 
pounds  at  each  single  stroke  of  the  piston. 

In  the  Table  No.  8  on  the  properties  of  saturated  steam, 
the  weight  of  a  cubic  foot  of  steam  of  this  pressure  is  found  to 


2IO  Steaui  Engine  Indicator 

be  .0511  pound,  and  the  heat  units  per  pound  1183.5;  hence 
the  cubic  foot  of  steam  from  which  the  mean  effective  pressure 
of  5  pounds  has  been  obtained,  contained  1 183.5  X  .0511  =  60.47 
heat  units. 

Now  instead  of  steam  of  20  pounds  pressure,  suppose 
steam  of  100  pounds  absolute  pressure  be  used:  Then  the 
mean  effective  pressure  would  be  100—  15  =  85  pounds. 

The  weight  of  a  cubic  foot  of  steam  of  100  pounds  pressure 
is  .2350  pounds  and  one  pound  contains  1213.8  heat  units. 
Then  as  before  12 13. 8x  .2330=282.8  heat  units  used. 

In  the  first  case  60.47  neat  units  have  been  used,  equal  to 
60.47-^5=12.09  heat  units  for  each  pound  mean  effective 
pressure;  whereas  in  the  second  case  282.8-^-85  =  3.32  heat 
units  for  each  pound  mean  effective  pressure  have  been  used. 

This  great  difference  and  discrepancy  in  the  two  instances, 
arises  from  the  fact  that  the  greater  part  of  the  total  heat  of 
the  steam  still  remains  in  it  at  the  pressure  of  the  exhaust,  (15 
pounds)  and  all  of  this  heat  is  entirely  lost  with  the  exhaust 
steam. 

The  only  heat  that  can  be  converted  into  useful  work,  is 
the  quantity  that  is  added  above  exhaust  pressure ;  therefore 
it  becomes  apparent  that  a  greater  per  cent  of  the  total  heat 
can  be  made  available,  as  the  pressure  increases. 

From  this  it  must  be  clearly  understood,  that  a  large  pro- 
portion of  the  heat  that  enters  into  the  steam  used  in  a  steam  en- 
gine is  requisite  in  order  to  raise  it  to  the  pressure  at  exhaust ; 
(15  pounds),  a  pressure  at  which  no  work  can  be  utilized  from  it. 

The  diagram  Fig.  104  fairly  illustrates  the  economy  of  the 
use  of  high  pressure  steam  in  a  cut-off  engine. 

The  full  lines  of  the  figure  represents  an  actual  diagram, 
and  above  it  the  shaded  portion  has  been  drawn  by  hand  to 
show  precisely  as  if  the  whole  of  the  diagram  had  been  taken 
at  a  higher  steam  pressure. 


And  Its  Appliances. 


211 


The  pressure  of  the  steatn  at  the  end  of  the  stroke,  or 
after  having  performed  all  of  the  work  there  is  in  it,  is  not 
changed ;  as  the  terminal  pressure  T  remains  the  same :  hence 
we  conclude  that  as  far  as  we  can  judge  by  the  diagram,  the 
work  represented  by  the  shaded  portion  could  be  done  without 
additional  expense. 

This  is  on  the  assumption  that  steam  expands  according  to 
the  Mariotte  law,  but  if  the  result  were  calculated  from  Table 


FIG.  104. 

No.  8  (properties  of  saturated  steam)  it  would  be  somewhat 
different,  but  we  have  no  positive  assurance  that  it  would  be 
any  more  correct ;  therefore  for  all  practical  purposes,  this 
presentation  of  the  subject  should  prove  acceptable. 

There  is  a  point  however  where  it  is  the  reverse  of  econom- 
ical to  run  at  very  high  pressures,  and  that  is  when  the  load 
on  the  engine  is  so  light,  and  cut-off  so  short,  that  the  steam 
expands  below  the  atmosphere,  and  thereby  forming  a  long 
loop  in  the  diagram  as  illustrated  in  Fig.  54  and  62. 


212  Steam  Engine  Indicator 

In  such  cases  the  engine  is  running  a  portion  of  each  stroke 
on  the  momentum  of  the  moving  parts. 

Where  this  occurs  it  is  better  to  reduce  the  boiler  pressure 
until  expansion  shall  come  quite  down  to,  but  not  below  the  at- 
mosphere. 

In  such  an  instance  a  considerable  advantage  is  realized  by 
reducing  the  speed  of  the  engine ;  as  the  resistance  of  the  atmos- 
phere must  be  overcome  in  running  an  underloaded,  as  well  as 
in  a  heavily  loaded  engine ;  therefore  by  reducing  the  speed  this 
factor  is  made  less,  and  on  lightly  loaded  engines  becomes  a 
considerable  percentage  of  the  total  power ;  this  percentage 
decreasing  in  extent  as  the  engine  is  more  heavily  loaded, 

In  connection  with  losses  from  having  under  loaded  en- 
gines, is  the  fact  also,  that  the  friction  of  the  engine,  conden- 
sation, etc.,  are  all  present  almost  regardless  of  the  load,  and 
always  appear  in  a  greater  proportion  in  light,  than  in  heavy 
loads ;  therefore  the  final  expense  is  decreased  when  running 
at  a  slower  speed ;  as  there  is  a  better  opportunity  to  secure  a 
later  cut-off,  since  the  power  bfeing  the  same,  with  reduced 
speed,  the  mean  effective  pressure  must  be  proportionally  in- 
creased . 


;#.  & 

•^i^ 


A  nd  Its  Appliances.  2 1 3 


CHAPTER    XXVI. 


THE    POINT   OF    CUT-OFF. 


It  must  not  be  understood,  (in  reference  to  steam  expan- 
sion) that  the  higher  the  grade  or  ratio  of  expansion,  the 
greater  is  the  economy,  because,  quite  the  reverse  may  often 
happen,  as  the  results  in  practice  are  greatly  modified  in  vari- 
ous ways  by  other  considerations. 

Consequently  the  most  economical  point  of  cut-off  will 
vary  in  different  types  of  engines,  in  accordance  with  the 
special  conditions,  and  circumstances  to  which  each  may  be 
subjected ;  such  as  high  or  low  initial  pressure,  condensation 
of  steam  in  the  cylinder,  different  methods  of  jacketing  and 
superheating,  amount  of  back  pressure  and  compression,  incor- 
rect adjustment  of  the  valves,  also  a  size  of  engine  that  is  not 
adapted  to  the  work,  etc.  ;  any  or  all  of  which  necessitates  a 
change  more  or  less  of  the  point  of  cut-off,  in  accordance  with 
any  particular  condition,  in  order  that  the  greatest  efficiency  of 
the  engine  may  be  realized. 

Initial  Pressure.  In  engines  with  an  early  cut-off,  and 
where  a  high  rate  of  expansion  prevails,  the  mean  or  average 
pressure  throughout  the  stroke  must  necessarily  be  low ;  and  a 
low  mean  pressure,  for  a  given  power  necessitates  the  use  of  a 
larger  engine. 

Also  a  high  rate  of  expansion  leads  to  a  low  terminal  pres- 
sure, and  to  expel  the  steam  from  the  cylinder  after  it  has 


2J4  Steam  Engine  Indicator 

performed  its  work,  will  require  from  one  to  three  pounds 
pressure  above  the  atmosphere ;  therefore  if  the  rate  of  ex- 
pansion be  such  that  the  terminal  pressure  falls  below  this, 
the  expansion  is  excessive,  and  the  reverse  of  advantageous. 

In  non-condensing  engines  the  lowest  possible  terminal 
pressure  coincides  with  the  pressure  of  the  atmosphere,  or 
about  I4TV  pounds  per  square  inch  absolute;  but  18  pounds 
may  be  considered  as  the  lowest  pressure  to  which  steam  can 
be  expanded  to  advantage ;  and  where  the  exhaust  passages 
are  small  and  tortuous,  or  where  the  exhaust  steam  contains 
considerable  moisture,  a  still  higher  terminal  pressure  will  be 
more  economical. 

In  condensing  engines,  the  temperature  in  the  condenser 
is  usually  about  100  degree  Fan.,  and  which  corresponds  to  a 
pressure  of  very  nearly  one  pound  to  the  square  inch ;  but  the 
presence  of  air  in  the  condenser  generally  prevents  the  pres- 
sure falling  below  two  pounds  per  square  inch. 

From  three  to  four  pounds  is  the  more  usual  and  may  be 
considered  as  the  lowest  advantageous  final  pressure,  to  secure 
the  best  economy.  The  highest  advantageous  rates  of  expan- 
sion with  jacketed  cylinders  appear  in  practice  to  be  between 
twelve  and  sixteen ;  but  in  unjacketed  or  exposed  cylinders, 
the  limit  of  advantageous  expansion  is  much  below  the  lowest 
of  the  rates  mentioned. 

The  principal  cause  of  the  discrepancy  between  the  theo- 
retical, and  actual  economy,  is  in  the  amount  of  heat  lost  in 
changing  the  water  in  the  cylinder  from  a  heated  liquid  state, 
to  the  condition  of  steam;  most  of  this  heat  passing  out 
with  the  exhaust  steam,  either  into  the  condenser  or  the  atmos- 
phere. It  has  been  fairly  well  demonstrated  by  frequent  tests, 
that  the  most  favorable  point  of  cut-off,  in  a  simple  non-con- 
densing engine,  is  usually  about  one-fourth  stroke,  when  using 
steam  of  from  80  to  90  pounds  per  square  inch  initial  pressure. 


A  nd  Its  Appliances.  215 

Where  the  cut-off  is  earlier  than  this  a  greater  per  cent  of 
loss  is  induced  through  cylinder  condensation ;  and  where  the 
cut-off  takes  place  later  in  the  stroke  there  is  also  an  increase 
of  loss,  from  the  fact  that  the  steam  is  exhausted  and  lost  while 
yet  at  a  considerable  pressure. 


FIG.  105. 

Fig.  105  is  a  fair  representation  of  an  indicator  diagram 
from  an  engine  working  under  the  favorable  conditions  men- 
tioned. 

The  results  of  some  recent  experiments  on  a  17  by  30  inch 
stroke  non-condensing  double  valve  engine  by  Prof.  J.  E. 
Denton,  to  determine  the  relation  of  steam  consumption  to 
point  of  cut-off  is  illustrated  by  the  graphical  diagram  Fig.  106. 

The  line  A.  B.  represents  the  stroke  of  the  engine,  which 
is  equally  divided  into  tenths  and  twentieths,  to  denote  the 
various  points  of  cut-off  in  fractions  of  the  stroke,  or  periods  of 
admission  of  steam  to  the  cylinder. 

From  each  of  these  fractional  parts  of  the  stroke  perpen- 
dicular lines  are  erected,  and  also  above  these  points  are  hori- 
zontal lines  laid  off  1-5  of  an  inch  apart;  each  representing  4 


216 


Steam  Engine  Indicator 


pounds,   or  a  scale  of  20  pounds  per  inch ;  being  the  actual 
pounds  of  water  used  per  horse  power  per  hour. 

Through  these  lines  three  curves  are  plotted,  being  the 
result  of  experiments  at  various  points  of  cut-off,  and  boiler 
pressure  by  which  the  change  in  the  rate  of  water  consump- 
tion, corresponding  to  changes  in  point  of  cut-off,  (as  well  as 
changes  in  boiler  pressure)  are  readily  observed. 


0.1       O.2      0.3      04      O.S      0.6       0.?      0.8       OJ       /.CO 

FIG.  106. 

The  three  curves  shown  in  the  diagram  corresponds  to  90, 
60,  and  30  pounds  boiler  pressure  respectively  per  square  inch, 
and  the  curves  were  constructed  by  locating  points  as  a  result 
of  tests  in  each  case  at  different  rates  of  cut-off.  It  will  be 
clearly  seen  that  the  curve  corresponding  to  90  pounds  per 
square  inch  boiler  pressure  and  the  steam  cut-off  at  ^,  or  -fJu 
of  the  stroke  gave  the  best  results,  and  represents  a  water  con- 
sumption of  about  26  pounds  per  horse  power  per  hour ;  that  for 


A  nd  Its  Appliances.  2 1 7 

60  pounds  pressure,  cut-off  at  -ff^  of  the  stroke  a  consumption  of 
about  32^  pounds,  and  that  for  30  pounds  pressure,  cut-off  at 
TVo  of  the  stroke ;  corresponds  to  a  consumption  of  43  pounds 
of  water  per  indicated  horse  power  per  hour. 

For  a  short  distance  on  either  side  of  these  points  of  cut- 
off, the  amount  of  water  consumption  is  only  slightly  increased 
and  the  economy  is  practically  the  same,  but  in  case  of  very 
early  or  very  late  cut-off  the  amount  of  water  consumed  is 
considerably  increased ;  the  relation  of  economy  to  cut- 
off being  well  represented  by  these  experiments  in  the 
diagram. 

In  some  similar  experiments  with  a  small  (7x14)  Buckeye 
automatic  non-condensing  engine,  with  a  boiler  pressure  of  75 
pounds,  the  same  experimenter  has  found  the  best  rate  of  con- 
sumption to  be  30  pounds  of  water  at  about  J^  cut-off;  and 
while  the  most  favorable  point  of  cut-off  is  the  same  in  small 
as  in  large  engines,  the  matter  of  economical  use  of  steam  is 
in  favor  of  the  larger  engine  and  high  pressure. 

It  should  be  understood  that  these  results  were  deduced 
from  refined  tests,  extending  over  a  considerable  period,  the 
engines  being  in  perfect  condition  as  to  leakage,  etc.,  and  the 
steam  collected,  condensed  and  carefully  weighed  after  the 
work  was  performed,  thus  eliminating  errors  as  far  as  possible. 

The  steam  was  also  practically  free  from  moisture,  as,  in 
the  tests  of  Fig.  106  it  contained  less  than  one  per  cent. 

From  these  and  other  similar  tests  we  are  enabled  to  form- 
ulate the  following  approximate  rule  for  best  cut-off. 

Divide  100  by  42  times  the  square  root  of  the  initial  pres- 
sure and  the  quotient  will  represent  the  most  favorable  point 
of  cut-off,  expressed  in  fractions  of  the  stroke.  The  initial 
pressure  must  be  reckoned  from  a  vacuum  for  condensing  and 
from  the  atmosphere  for  non-condensing  engines. 


2 1 8  Steam  Engine  Indicator 

In  a  test  for  ascertaining  the  economy  of  engines,  it  is  very 
important  that  the  quality  of  the  steam  used,  or  in  other  words 
the  amount  of  moisture  it  contains,  be  determined. 

This  quantity  may  be  approximately  found  by  making 
what  is  known  as  a  calorimeter  test,  as  explained  in  Chapter 
XXX. 

There  are  a  number  of  instruments  of  varied  construction 
and  principle,  on  the  market  for  this  purpose,  with  full  and 
complete  instructions  for  their  use. 

In  the  absence  of  such  a  test,  no  accurate  conception  of 
the  amount  of  steam  actually  used  by  the  engine  to  produce  a 
liorse  power  per  hour,  can  be  obtained,  for  the  steam  may  con- 
tain a  large  amount  of  ineffective  moisture  in  the  form  of  spray, 
which  can  only  be  detected  either  by  an  application  of  the 
calorimeter,  or  by  collecting  and  weighing  the  exhaust. 

The  generally  acknowledged  economy,  that  has  been  at- 
tained in  the  steam  engine  within  the  last  thirty  years,  (esti- 
mate between  thirty  and  forty  per  cent.)  may  be  considered 
due,  principally  to  the  employment  of  multiple  cylinder  engines 
in  connection  with  the  best  modern  method  of  jacketing :  also 
an  increase  of  steam  pressure,  and  superheating  the  steam ; 
either  or  all  of  which  (when  judiciously  made  use  of)  tends  to 
better  efficiency,  and  more  economical  results. 


.         . 

Mr  #. 

«/  \w 


A  nd  Its  Appliances.  2  1 9 


CHAPTER  XXVII 


BACK   PRESSURE   AND    COMPRESSION. 


Back  Pressure  may  be  considered  as  one  of  the  most  serious 
losses  in  an  engine,  and  represents  the  power  expended  in  ex- 
pelling the  exhaust  steam,  and  in  compressing  steam  into  the 
clearance  spaces,  and  is  usually  called  the  loss  from  back  pres- 
sure, for  it  must  be  clearly  understood  that  the  direct  steam 
does  work  in  expelling  the  exhaust  from  the  engine,  as  well  as 
in  driving  the  machinery  to  which  the  engine  is  connected. 

The  whole  of  the  back  pressure  cannot  be  removed,  but  a 
large  proportion  of  the  present  losses  would  be  avoided,  if  the 
clearance  spaces  were  reduced  to  the  smallest  practical  dimensions. 

The  following  diagrams  Figs.  107  to  1 10  will  serve  to  illus- 
trate the  economy  to  be  derived  where  small  clearances  prevail. 

The  diagrams  referred  to,  are  theoretical,  but  in  each  case 
the  assumed  clearances  (Fig.  107  being  seven  per  cent,  and  Fig. 
109  being  only  two  per  cent.)  are  exactly  with  many  of  those 
found  in  different  makes  of  slow  speed  engines. 

To  obtain  the  maximum  economical  results  with  an  engine 
at  any  given  cut-off,  compression  should  be  carried  up  to,  or 
very  nearly  the  initial  pressure  of  the  cylinder. 

Where  the  clearances  are  large  however,  this  is  not  always 
possible,  especially  with  condensing  engines,  and  without 
much  consideration  of  the  subject  many  builders  of  engines 
adjust  the  valve  so  that  compression  begins  at  about  seven- 
eighths  of  the  stroke. 


220 


Steam  Engine   Indicator 


In  the  diagrams  the  various  compression  lines  are  shown, 
and  the  results  compared.  The  initial  pressure  is  100  pounds 
above  zero  in  all,  and  the  cut-off  takes  place  at  one-quarter 
stroke  in  each,  so  that  when  compression  is  carried  up  to 
initial  pressure,  the  same  quantity  of  steam,  practically,  is 
used  per  stroke  in  each  engine  irrespective  of  clearance,  but 
the  net  power  developed  under  those  circumstances  will  differ 
very  materially. 

The  exhaust  lines  in  the  non-condensing  diagrams  are  0.3 
pounds  above  atmosphere  or  1 5  pounds  above  zero,  and  in  the 
condensing  diagrams  3.5  pounds  above  zero,  or  11.2  pounds 
below  atmosphere. 


FIG.  107. 

THEORETICAL   DIAGRAM   WITH   7   PER   CENT   CLEARANCE. 

In  Fig.  107  the  solid  lines  represent  diagrams  from  a  non- 
condensing  engine  with  compression  A  to  initial  pressure,  and 
also  compression  B  to  50  pounds,  or  one-half  the  initial  pres- 
sure. 

The  dotted  lines  represent  the  back  pressure  lines  of  dia- 
grams from  a  condensing  engine,  A  i,  represents  compression 
to  initial  pressure;  B  i,  compression  to  50  pounds,  and  C, 
compression  to  14  pounds. 


And  Its  Appliances.  221 

The  initial  pressure  of  theoretical  diagram  Fig.  107  is  100 
pounds  above  zero ;  cut-off  one-quarter  stroke ;  terminal  pres- 
sure 30  pounds  above  zero,  back  pressure  non-condensing,  15 
pounds  and  condensing  3.5  pounds  above  zero. 

From  these  diagrams  the  Available  Power  may  be  ascer- 
tained, which  includes  the  amount  absorbed  in  driving  the 
engine  as  well  as  the  effective  power,  and  is  usually  designated 
ihe  Indicator  Horse  Power,  and  written  I.  H.  P. 

This  is  not  the  total  power  derived  from  the  steam,  but 
the  I.  H.  P.  must  be  known  in  order  to  ascertain  the  loss. 

The  total  power  diagram  of  Fig.  107  is  shown  by  the  full 
lines  in  Fig.  108  and  is  determined  as  follows :  During  a  single 
stroke  of  the  engine  piston,  the  indicator  on  that  side  where 
the  steam  is  admitted  will  trace  the  upper  line  only  of  the  dia- 
gram, the  lower  line  being  zero. 

The  pressure  of  steam  during  that  stroke  being  measured 
from  the  zero  line  (by  the  scale  of  the  spring)  consequently  the 
total  power  exerted  by  the  steam  is  proportional  to  the  area 
enclosed  between  the  zero  line  and  the  upper  line  of  the  dia- 
gram. 

If  an  indicator  be  placed  in  communication  with  the  other 
side  of  the  piston  during  the  same  stroke  it  will  make  the 
lower  line  only,  or  the  back  pressure  line,  (represented  by  the 
dotted  lines  in  Fig.  108)  of  the  indicator  diagram.  This  line 
also  in  connection  with  the  zero  line  forms  another  diagram, 
and  the  area  enclosed  between  these  lines,  represents  the  power 
necessary  to  expel  the  exhaust  steam  during  the  first  part  of  the 
stroke,  and  to  compress  steam  into  the  clearance  spaces  during 
the  latter  part. 

The  full  lines  of  the  diagram  Fig.  108  show  the  total 
power  exerted  by  the  steam,  and  the  dotted  lines  show  back 
pressure  from  exhaust,  and  compression,  or  the  resistance 


222  Steam  Engine  Indicator 

which  the  direct  steam  must  overcome  before  any  useful  work 
can  be  accomplished. 

The  difference  between  the  two  is  the  power  that  must 
be  expended  before  any  is  available  for  running  the  engine  or 
driving  the  machinery  and  is  a  total  loss. 


FIG.  108. 

It  is  evident  at  a  glance  of  the  diagram  Fig.  108  that  this 
loss  is  a  large  proportion  of  the  total  power  and  every  means 
that  will  tend  to  reduce  this  loss  should  be  adopted. 

As  before  mentioned  the  whole  of  this  cannot  be  avoided, 
because  it  is  impossible  to  obtain  a  perfect  vacuum  in  an  engine 
cylinder ;  however  the  back  pressure  should  be  as  low  as  pos- 
sible, bearing  in  mind  that  the  clearance  spaces  should  be  filled 
with  steam  compressed  (as'  near  as  possible)  to  the  initial  pres- 
sure at  the  end  of  the  stroke. 

In  the  case  of  condensing  engines  having  large  clearances, 
this  latter  condition  is  difficult  of  attainment,  and  if  strictly 
carried  out  would  probably  entail  so  much  loss  from  increased 
back  pressure  as  to  off-set  any  gain  from  high  compression. 

This  points  to  the  benefit  of  small  clearances  with  which 
compression  may  be  carried  to  any  desired  pressure. 

In  Fig.  107  the  mean  effective  pressure  of  the  non-con- 
densing diagram  compressed  to  initial  pressure,  (as  line  A),  is 


A  nd  Its  Appliances.  225 

41  6  pounds,  while  the  average  pressure  of  the  total  power 
diagram  Fig.  108  is  64  pounds,  or  about  54  per  cento  greater 
than  the  available  power. 

In  this  case  the  only  way  of  reducing  the  back  pressure  is- 
to  commence  compression  later  in  the.  stroke  as  shown  by  line  B. 

The  effect  of  this  however,  is  a  loss  from  low  compression, 
as  this  is  only  carried  to  50  pounds,  and  also  from  increased 
condensation. 

By  comparing  the  results  from  the  two  diagrams  it  will  be 
found  that  the  latter  has  a  mean  effective  pressure  of  47 
pounds,  making  a  gain  in  pressure  of  about  1 3  per  cent  over 
that  of  the  former  but  there  would  be  14  per  cent  more  steam 
necessary  to  fill  clearance  spaces,  and  the  condensation  would 
be  increased  more  than  4  per  cent.,  making  a  loss  of  5  per 
cent,  by  not  compressing  to  initial  pressure. 

If  this  engine  was  condensing  it  would  be  practically  im- 
possible to  compress  to  initial  pressure  as  in  order  to  do  so,  it 
would  be  necessary  to  begin  compression  at  the  commencement 
of  the  stroke  with  a  pressure  of  6. 5  pounds,  above  zero  (line 
A  i),  therefore  8.2  pounds  would  be  the  maximum  vacuum  that 
could  be  obtained  in  the  cylinder ;  consequently  the  highest 
pressure  to  which  compression  can  be  carried  practically  in  this 
case  is  one-half  the  initial  pressure  or  50  pounds  above  zero 
(line  B  i). 

The  mean  effective  pressure  of  this  diagram  is  54.3  Ibs. 
and  the  total  power  diagram  as  shown  in  Fig.  108  is  64  pounds 
or  about  18  per  cent,  greater;  however  there  would  be  14  per 
cent,  more  steam  required  than  when  compressing  to  initial 
pressure,  and  condensation  would  be  increased  fully  4  per  cent. 

If  compression  did  not  commence  until  later  in  the  stroke 
and  only  carried  up  to  14  pounds  (line  C),  the  mean  effective 
pressure  would  be  59.6  pounds  or  9.8  per  cent,  more  than  the 
previous  diagram,  but  over  24  per  cent,  more  steam  would  be 
required  than  if  compression  were  carried  to  initial  pressure,. 


224 


lii tain  Engine  Indicator 


and  the  extra  condensation  would  amount  to  6.9  per  cent,  or  a 
loss  of  3  per  cent,  over  the  previous  diagram  with  greater  com- 
pression. 

Comparing  the  later  diagram  (line  C),  with  the  total  power 
it  will  be  seen  that  the  total  power  is  but  7.5  per  cent,  greater, 
and  it  is  this  near  approach  to  the  total  diagram,  that  makes 
the  condensing  engine  so  much  more  economical  than  the  non- 
condensing,  and  a  moderately  well  loaded  engine  gives  better 
results  than  one  lightly  loaded,  as  in  the  case  of  a  lightly 
loaded  engine,  the  waste  power  remains  the  same,  and  conse- 
quently the  percentage  of  loss  increases ;  although  both  the 
total,  and  available  power  are  less. 

In  the  first  diagram  the  steam  developed  over  3  horse- 
power to  make  2  horse  power  available,  or  a  loss  of  35  per  cent. 
In  some  very  lightly  loaded  engines,  the  steam  develops  over  3 
horse  power  to  make  i  horse  power  available,  or  a  loss  of  70 
per  cent. 


FIG.  109. 
THEORETICAL  DIAGBAM  WITH  2  PEE  CENT  CLEARANCE. 

Initial  pressure  100  pounds  above  zero:  cut-off,  one-quar- 
ter stroke ;  terminal  pressure  30  pounds  above  zero ;  back 
pressure  non-condensing  15  pounds  and  condensing  3.5  pounds 
above  zero.  In  Fig.  109  as  in  Fig.  107  the  full  lines  represent 


And  Its  Appliances.  22$ 

diagrams  from  a  non-condensing  engine  with  compression  A 
to  initial  pressure,  and  compression  B  to  50  pounds  above 
zero. 

The  dotted  lines  represent  the  back  pressure  lines  of  con- 
densing diagrams,  with  compression  A  i,  to  initial  pressure, 
also  compression  B  i,  to  50  pounds  pressure  and  compression 
C  to  14  pounds  above  zero;  therefore  the  two  diagrams  Figs. 
107  and  109  are  identical  in  all  respects  except  in  their  amount 
of  clearance. 

The  total  power  diagram  of  Fig.  109  is  shown  in  full  lines 
in  Fig.  1 10,  and  the  back  pressures  and  the  compression  curves 
are  shown  by  the  dotted  lines  A,  A  i,  B,  B  i,  and  C. 

•    The  mean  effective  pressure  being  determined  in  the  same 
manner  as  in  the  previous  diagrams. 

In  Fig.  109  the  mean  effective  pressure  of  the  non-con- 
densing diagram  compressing  to  initial  pressure  (line  A)  is  44 
pounds  and  the  average  pressure  of  the  total  power  diagram 
Fig.  1 10  is  60.8  pounds  or  about  38.5  per  cent  greater  than  the 
available  power. 

This  is  quite  a  loss,  but  it  is  a  decided  improvement  over 
the  percentage  of  loss  shown  by  the  diagram  with  large  clear- 
ance, as  in  Fig.  107. 

If  in  this  case  the  compression  had  been  carried  to  50 
pounds  only,  (line  B),  the  mean  effective  pressure  would  have 
been  45.6  pounds  or  3.6  per  cent,  greater  pressure,  but  there 
would  be  over  4  per  cent,  more  steam  required  to  fill  the  clear- 
ance spaces,  and  the  condensation  would  be  increased  over  3 
per  cent.,  making  a  loss  of  about  3. 5  per  cent,  by  the  lower 
compression. 

With  the  condensing  diagram  Fig.  109  it  will  be  seen  that 
compression  may  be  carried  to  initial  pressure,  (line  A)  and  the 
mean  effective  pressure  in  this  case  would  be  52.8  pounds. 

If  the  compression  had  been  carried  to  50  pounds  only, 
(line  B),  the  mean  effective  pressure  would  have  been  56 


226  Steam  Engine  Indicator 

pounds,  or  an  increase  of  6  per  cent,  in  the  pressure ;  but  as  an 
off-set,  over  4  per  cent,  more  steam  would  be  required  to  fill  the 
clearance  space,  and  the  condensation  would  be  increased  more 
than  3  per  cent.,  leaving  a  loss  of  i  per  cent. 

If  the  compression  had  been  still  lower,  (line  C),  the  mean 
effective  pressure  would  have  been  57.5  pounds,  or  an  increase 
of  8  per  cent,  in  the  pressure ;  but  there  would  be  7  per  cent, 
more  steam  required  to  fill  the  clearances,  and  condensation 
would  be  increased  over  5  per  cent.,  making  a  loss  of  4  per 
cent,  by  the  low  compression. 

Comparing  the  results  obtained  from  the  two  diagrams, 
the  saving  effected  by  an  engine  having  small  clearance  will 
readily  be  seen,  and  as  this  has  such  an  important  bearing  on 
the  economy  of  the  engine,  small  clearances  should  be  strictly 
insisted  upon. 

There  are  many  slow  speed  engines  in  use  at  present  hav- 
ing less  than  3  per  cent,  clearance,  and  this  amount  should 
therefore  be  the  maximum  allowed  in  slow  speed  engines, 
either  simple  or  compound. 


FIG.  110. 

Full   lines   show   theoretical   diagram    of    total    pressure 
exerted  by  the  steam. 


A  nd  Its  Appliances .  227 

Dotted  lines  show  back  pressure  from  exhaust  and  com- 
pression, or  the  resistance  which  the  direct  steam  must  over- 
come, before  any  useful  work  can  be  accomplished. 

COMPARISON  OF  RESULTS. 


Non-Condensing  'Diagrams. 

Clearance     .....     >     .     .     7$    .....     2% 

Cut-Off   .........   25^    .....  25% 

Terminal  Pressure    .....   3olbs.  above  zero  26-slbs.  above  zero. 

Back  .     .     .     .     .   islbs.     "          " 


M.E.P.  M.E.P. 

Compression  to  Initial  pressure  and  Gain  compared  with 

using  equal  quantities  of  steam  larger  clearance. 

per  stroke  in  both  engines  ...  41  -6lbs.     .     .     .     44lbs.  5  -8$ 

Loss    by    Compressing    to    solbs 

pressure  in   place  of  full   Com- 

pression .........   5#    .....     3'5#  7-3$ 

Condensing  Diagrams. 

Clearance  .....     ....     7^  .....        2% 

Cut-Off  ..........  25£  .....  25^ 

Terminal  Pressure  ......  3olbs.  above  zero  26  -slbs.  above  zero. 

Back  "          ......  3'Slbs.     "       "  3'5lbs. 

Gain  compared  with 
larger  clearance. 

Compression  to  Initial  pressure  .  —  8$ 

Loss  by  Compressing  to  solbs. 

pressure  in  place  of  full   Com- 

pression .........  6#  \%  13$ 

Loss  by  Compression  to  i4lbs. 

pressure  in  place  of  full   Com- 

pression .........  9%  4%  13$ 

In  Compound  Engines  the  greater  economy  will  be  obtained 
when  expansion  is  carried  down  to  the  back  pressure  in  each 
cylinder,  except  the  last,  and  Compression  is  carried  up  to  In- 
itial pressure  in  all  ;  with  no  drop  or  free  expansion  between 
the  cylinders. 


22 8  Steam  Engine  Indicator 


CHAPTER  XXVIII. 


COMBINING   DIAGRAMS     FROM    COMPOUND    ENGINES 


Compound  engines,  for  almost  all  purposes  are  now  com- 
ing into  more  general  use  each  year ;  but  in  the  use  of  the  in- 
dicator upon  them,  both  cylinders  are  treated  as  simple  engines, 
the  power  of  each  being  added  together. 

The  diagrams  from  both  cylinders  can  be  taken  with  the 
same  denomination  of  spring  if  desired,  but  usually  a  compar- 
atively light  spring  is  used  on  the  low  pressure  in  order  that 
the  dimensions  or  area  of  the  diagram  may  be  increased. 

The  compound  engine  with  receiver,  is  as  two  engines, 
one  high  pressure  non-condensing,  and  the  other  a  low  pres- 
sure condensing  engine,  but  from  the  fact  that  the  same  steam 
is  used  in  both  cylinders,  the  action  of  the  steam  must  be  con- 
sidered as  if  used  in  a  single  engine,  and  the  diagrams  from 
each  cylinder  must  be  combined,  to  form  an  equivalent  simple 
one. 

Before  making  combinations  of  diagrams  from  the  high 
and  low  pressure  cylinders  of  compound  engines,  the  object  of 
combining  them  should  be  first  understood. 

There  are  certain  losses  in  single  or  non-compound  en- 
gines which  are  corrected  to  a  great  extent  by  compounding, 
but  this  in  turn  introduces  other  losses  which  it  is  desirable  to 
reduce  to  the  least  possible  amount. 


And  .Its  Appliances.  229 

These  losses  are  between  the  two  cylinders,  and   consist 
of,  condensation  in  the  passages,  pipes,  and  receiver  (if  one  be 
used),  friction  in  the  steam  ports  and  pipes,  and  expansion  of 
the  steam  that  takes  place  between  the  two  cylinders  without 
doing  useful  work. 

The  extent  of  these  losses  can  be  shown  by  combining  the 
diagrams  'i'roni  the  two  cylinders  and  drawing  in  the  hyper- 
bolic curve.  This  curve  should  just  touch  the  expansion  line 
of  the  high  pressure  diagram  at  a  point  where  the  exhaust 
from  the  cylinder  begins,  and  the  space  between  the  curve  and 
both  diagrams  below  this  point,  and  also  the  space  between  the 
two  diagrams,  represent  the  loss  between  the  two  cylinders. 

To  correctly  combine  the  two  diagrams,  the  clearance  in 
each  cylinder  should  be  known  and  accounted  for,  as  well  as 
the  piston  displacement,  and  the  relative  length  of  the  two 
diagrams  when  combined,  is  as  the  ratio  of  the  total  volume  of 
the  cylinders,  that  is ;  the  piston  displacement  plus  the  clear- 
ance at  one  end. 

To  do  this,  a  base  line  may  be  taken  if  desired  and  divided 
into  two  parts,  which  have  the  same  relation  to  each  other  in 
length,  as  the  total  volume  of  the  cylinders.  The  short  por- 
tion of  the  line  will  represent  the  small  or  high  pressure  cylin- 
der, and  on  this  length  the  diagram  from  this  cylinder  is  con- 
structed from  the  lowest  pressure,  and  on  the  longer  portion  of 
the  line  the  diagram  from  the  large  cylinder  is  laid  out. 

It  is  best  however  to  decide  on  the  total  length  of  the  low 
pressure  diagram  first,  and  a  length  that  can  be  easily  divided 
into  100  parts  will  be  found  most  convenient,  as  percentages>of 
this  length  can  then  be  easily  measured;  for  example,  10  inches 
for  a  scale  of  tenths,  or  12^  inches  for  a  scale  of  eighths.  The 
combination  diagram,  Fig.  113,  was  drawn  12^  inches  long, 
and  photo  reduced  to  the  length  shown. 

It  now  becomes  necessary  to  decide  on  the  scale  of  the 
spring  to  which  the  two  diagrams  are  to  be  plotted ;  usually  it 


230 


Steam  Engine  Indicator 


will  be  found  most  convenient  for  this  to  take  the  scale  of  the 
low  pressure  diagram ;  then  draw  in  the  atmospheric,  and  va- 


FIG.  111. 


2[        4\         3j         4j         f\          *\          7J 

FIG.  112. 

cuum  lines,  and  erect  perpendiculars  at  the  two  extremes  of 
the  combination  diagram,  one  of  which  is  the  clearance  line. 

All  measurements  of  distance  should  be  made  from  the 
clearance  line,   and   all  measurements  of    pressure    from  the 


And  Its  Appliances. 


231 


atmospheric  line.  Now  divide  each  original  diagram  into  any 
desired  number  of  equal  parts,  10  being  a  good  number. 

Find  the  volume  of  the  piston  displacement  of  the  low 
pressure  cylinder,  to  which  add  the  volume  of  the  clearance ; 
the  total  length  of  the  diagram  represents  this  total  volume. 

Divide  the  clearance  by  the  total  volume,  and  the  quotient 
will  be  the  percentage  this  clearance  bears  to  the  whole  length. 


FIG.  113. 

Set  off  this  distance  from  the  clearance  line,  and  divide 
the  remainder  (representing  the  piston  displacement)  into  the 
same  number  of  parts  that  the  original  diagram  is  divided  into. 

If  the  scale  selected  is  the  same  as  that  of  the  original  dia- 
gram, simply  transfer  the  pressures  directly  with  a  pair  of  di- 
viders from  the  lines  on  the  original  diagram  to  the  corres- 
ponding lines  on  the  combination  ;  then  draw  in  the  connecting 


232  Steam  Engine  Indicator 

portions  of  the  diagram,  and  the  result  will  be  an  elongated 
diagram  from  the  low  pressure  cylinder  or  as  if  it  had  been 
taken  with  the  same  spring  as  before,  but  with  a  proportion- 
ately enlarged  paper  drum. 

Now  find  the  total  volume  of  the  high  pressure  cylinder, 
and  divide  it  by  the  total  volume  of  the  low  pressure  cylinder, 
and  the  quotient  is  the  percentage  of  length  of  the  diagram, 
which  should  be  measured  from  the  clearance  line. 

Divide  the  clearance  volume  of  the  high  pressure  cylinder 
by  the  total  volume  of  the  low  pressure  cylinder  and  measure 
off  the  percentage  of  length,  as  before,  from  the  line. 

Divide  the  remaining  length  of  the  high  pressure  diagram 
(representing  the  piston  displacement)  into  the  same  number 
of  parts  as  the  original  diagram,  and  transfer  the  pressures 
from  the  lines  on  the  original  diagram  to  the  corresponding 
lines  on  the  combination  and  to  the  new  scale  of  pressures. 

If  the  original  high  pressure  diagram  was  taken  with  a  40 
spring,  and  the  combination  diagram  made  to  a  scale  of  iclbs. 
per  inch,  then  the  new  diagram  will  be  four  times  as  high  as 
before,  although  it  may  be  shorter. 

Next  draw  in  the  hyperbolic  curve ;  (a  method  of  doing 
this  is  given  on  page  101,  Fig.  56)  and  the  two  diagrams  thus 
combined  will  form  a  single  one. 

The  process  of  combining  indicator  diagrams  from  com- 
pound engines  is  both  interesting,  and  instructive  to  the  en- 
gineer in  various  ways,  and  usually  attended  with  most  satis- 
factory results. 

Diagram  Fig.  113  is  a  combination  of  the  diagrams  Figs. 
1 1 1  and  112,  and  were  taken  from  a  tandem  compound  engine. 

In  order  to  make  the  foregoing  explanation  more  clearly 
understood,  diagrams  Figs,  in,  112  and  113  have  the  con- 
struction lines  shown,  and  the  necessary  calculations  are  given 
below.  Fig.  113  was  drawn  i2j^  inches  long  over  all  and  re- 
duced by  photo  engraving  process  to  its  present  length. 


And  Its  Appliances  .  233 

Diameter  of  H.  P.  Cylinder       -        -  30  in. 

11  L.  P.          "  50  in. 

Stroke  of  Pistons                                   *  72  in. 

Diam.  of  Piston-rod,  both  Cylinders  6^  in. 

Volume  of  High  Pressure  Cylinder  — 

(706*86—  30-68)  X  72  =  48685  cubic  inches. 

Clearance   volume  =   2545     "  " 

Total  volume  51230 
Volume  of  Low  Pressure  Cylinder  — 

(1963-50—  30-68)  X  72=  139163  cubic  inches. 
Clearance  volume      =     7673     "  " 

Total  volume   146836 
Total  length  of  L.P.  card,  12%  inches,  or  100  eights;   scale 

10.   Length  of  L.P.  clearance,  marked  A  on  diagram,  Z_?3X  __i 

146836 


=  5-22$  of  total  length  or  l  +  ^in.  The  remainder  of  the 
length,  representing  the  piston  displacement,  is  divided  into 
10  parts,  the  same  as  original  diagram,  and  the  pressures  trans- 
ferred to  the  corresponding  lines. 

Total  length  of  H.P.  card,  or  B+C  on  diagram,  5123°><ioo 

246830 
=  34-89$,  or  4f|  in.     Length  of  H.P.  clearance,  marked  B  on 

diagram,         \0   .,     =i'73#,    or    F%  in.,    leaving    the    distance 
140830 

marked  C,  representing  the  piston  displacement,  which  is  di- 
vided to  correspond  with  the  original  diagram,  and  the  pres- 
sures transferred  either  with  scales  or  dividers  ;  in  the  latter 
case  each  distance  must  be  multiplied  four  times.  Draw  in 
the  connecting  portions  of  the  diagrams,  taking  care  to  follow 
the  contour  of  the  original  as  closely  as  possible  ;  and  finally 
the  hyperbolic  curve  is  drawn  in, 


234  Steam  Engine  Indicator 


CHAPTER  XXIX. 


DIAGRAMS   FROM    GAS  AND    OIL   ENGINES   AND   AMMONIA 
COMPRESSORS. 


In  the  last  few  years  the  large  increase  in  the  number  of 
gas  and  oil  engines  in  use  for  all  kinds  of  manufacturing  enter- 
prises both  at  home  and  abroad,  has  been  most  remarkable,  and 
their  number  and  power  are  still  increasing  each  year,  so  that 
now  these  motors  are  in  competition  with  steam  engines  in 
almost  all  progressive  countries. 

The  fact  that  both  gas  and  oil  engines  now  run  with 
greater  regularity  than  in  the  past  is  principally  due  to  im- 
proved and  better  governing  arrangements.  The  portability 
of  small  oil  engines  renders  them  very  convenient  for  use  in 
country  towns,  and  other  places  where  gas  is  not  made.  A 
greater  part  of  these  motors  work  with  the  four-cycle,  and  with 
lift  valves. 

Gas  engines  are  in  most  cases  single  acting  and  single  cyl- 
inder, except  for  the  largest  powers,  when  two  cylinders  are 
generally  used. 

The  charge  is  usually  fired  either  by  tube  ignition,  or  b} 
an  electric  current.  The  piston  speed  usually  varies  from  500 
to  700  feet  per  minute,  and  the  clearance  volumes  of  the  cylin- 
der are  much  larger  than  in  steam  engines,  usually  from  20  to 
50  per  cent,  of  the  piston  displacement,  against  from  3  to  8 
per  cent,  in  steam  engines. 


A  nd  Its  Appliances. 


235 


When  considering  that  in  the  employment  of  gas  engines 
no  fuel  is  being  consumed  when  the  engine  is  not  in  actual 
operation,  it  is  evident  that  they  form  economical  motors  when 
small  powers  are  required,  and  will  soon  come  into  more  ex- 
tensive  use  as  affording  a  cheap,  and  efficient  motive  power  in 
a  great  number  of  places  where  the  use  of  steam  is  difficult  or 
impossible. 

Owing  to  the  greatly  increased  initial  pressure  in  the  cyl- 
inders of  these  engines,  (being  principally  due  to  the  explosive 
mixture  employed  therein)  specially  designed  indicators  have 
been  constructed  to  better  meet  the  requirements  necessary, 
and  provide  means  for  indicating  pressures  ranging  from  300 
to  600  or  more  pounds  pressure  per  square  inch. 

This  is  accomplished  by  making  provision  in  the  construc- 
tion of  the  instrument,  whereby  a  piston  can  be  used  of  a  small- 
er size  than  the  piston  of  one-half  square  inch  in  area,  as  ord- 
inarily used  in  most  makes  of  indicators.  This  smaller  piston  is 

usually  made  one-quarter  of  a  sq.inch 
in  area,  or  one-half  that  of  the  former, 
and  which  when  in  use,  results  in 
doubling  the  readings  or  amount  of 
pressure,  as  when  used  with  the 
same  denomination  of  spring  in  con- 
nection with  the  larger  piston.  Fig. 
114  represents  the  manner  of  con- 
struction in  combining  the  half  and 
quarter  inch  area  piston  in  one  in- 
strument, as  applied  to  the  Tabor 
Indicator,  whereby  the  use  of  the 
one-half  inch  piston  for  low  pres- 
sures, or  in  which  the  quarter  inch 
piston  may  be  used  for  the  very  high 
FlG-  1U-  pressures  often  attained  in  some  oil 

and   gas   engines.       Either   of    these    pistons    may    be   used 


236  Steam  Engine  Indicator 

independently  as  desired,  without  any  change  whatever  either 
in  the  spring  or  any  part  of  the  instrument. 

In  the  illustration  the  half  inch  piston  is  not  shown ;  but 
instead  the  quarter  inch  piston  is  represented  attached  to  the 
spring  in  position  for  operation. 

The  body  A.  of  the  instrument  is  shown  partly  in  section 
in  order  that  the  location  of  the  parts  may  be  readily  observed. 
B.  is  the  piston  cylinder  in  which  the  half  inch  piston  works, 
and  which  is  srcewed  at  its  lower  end  into  the  body  A.  C.  is 
the  piston  cylinder  in  which  the  quarter  inch  piston  works, 
and  is  formed  in  the  upper  end  of  the  tube  G. 

D.  is  the  quarter  inch  piston,  and  is  sufficiently  elongated 
as  to  reach  and  work  in  the  cylinder  C.  Its  upper  end  is 
threaded  and  screws  into  the  mounting  of  the  indicator  spring. 
It  is  made  in  the  form  of  a  shell,  and  the  pencil  mechanism  is 
secured  to  it  by  means  of  the  extended  thumb-nut  E.  F.  is 
the  usual  connection  for  securing  the  indicator  to  the  cock. 
H.,  I.  and  J.  are  respectively  the  cylinder  cap,  swivel  plate 
and  piston  rod. 

In  addition  to  obtaining  the  most  accurate  results  from 
high  pressures  by  the  use  of  the  smaller  size  of  piston,  this 
combined  indicator  has  another  advantage  in  that  it  requires  a 
less  number  of  springs  for  any  given  range  of  pressure. 

For  example  :  A  50  spring  may  be  used  in  connection  with 
the  larger  piston  to  120  pounds  pressure  per  square  inch,  but 
by  substituting  the  smaller  piston,  pressures  may  be  indicated  to 
240  pounds  with  the  same  denomination  of  spring ;  a  range 
that  would  otherwise  require  two  springs ;  thereby  doubling 
the  range  of  the  instrument  with  a  single  spring.  Figs.  1 1 5  to 
1 1 8  inclusive  represent  diagrams  taken  from  the  Springfield  Gas 
and  Gasolene  engines.  Fig.  115  is  from  a  7^  inch  diameter 
of  cylinder  by  14  inches  stroke,  running  200  revolutions  per 
minute,  with  scale  of  spring  120. 


And  Its  Appliances. 


237 


Fig.  116  is  from  a  13  inch,  diameter  of  cylinder  by  24 
inches  stroke,  running  160  revolutions  per  minute,  with  the 
scale  of  spring  120. 


FIG.  115. 

Each  of  the  above  may  be  considered  as  ideal  cards  in 
every  respect.     Figs.  117  and   118  are  from  gasolene  engines 


FIG.  116. 

presented  simply  for  the  purpose  of  showing  some  bad  cards. 
Fig.  117,   shows  the  effect  of  late  ignition,  while   Fig.    118, 


238  Steam  Engine   Indicator 

shows  also  late  ignition,  and  a  stratified  condition  of  the 
charge.  This  is  indicated  by  the  waving  expansion  line,  each 
waving  being  an  independent  explosion  or  combustion. 


FIG.  117. 

These  two  latter  cards  were  taken  expressly  for  the  pur- 
pose of  showing  these  very  things.  Fig.  1 19  represents  a  pair 
of  superimposed  indicator  diagrams  taken  from  a  20  by  26  inch 
steam  cylinder,  driving  a  double-acting  ammonia  compressor 
from  a  Buffalo  Refrigerating  plant,  making  26  revolutions  per 
minute,  and  are  ideal  diagrams  in  almost  every  respect.  How- 
ever where  the  speed  of  the  engine  is  slow,  as  in  refrigerating 
machines  they  are  only  what  might  be  expected,  as  the  exist- 


FIG.  118. 

ing  conditions  are  generally  favorable  for  the  production  of 
good  diagrams ;  because  a  longer  interval  of  time  is  given  to 
the  steam  to  pass  through  the  steam  ports  and  fill  the  cylinder 


And  Its  Appliances. 


239 


nearly  to  boiler  pressure  at  the  commencement  of  the  stroke, 
and  thus  continue  to  the  point  of  cut-off;  and  where  the  steam 
admission  is  regulated  by  an  automatic  system  of  valve  gears 
(such  as  in  this  case)  we  find  the  cut-off  well  defined,  the  ex- 

SCALE,  40  Lfia.  i-i-B  8(4.  i.scu. 


Steam  Pressure .75  Ibs. 

Revolutions _.26p«*mln. 

Indicated  Eoree  Power 


'Bottom  end. 


Steain  Cylinder, . 


FIG.  119. 

pansion  line  all  that  could  be    desired,  and   the  back   pressure 
line  nearly  straight. 

Figs.  120  and  121  represents  diagrams  taken  from  the  gas 
or  ammonia  cylinder  which  is  15  inches  in  diameter  by  26  inch. 

SOAUC,  SO  LB8.  FEB  Sq.  I* OH. 


Discharge  Pressure. _ laoiba. 

Suction  Pressure _ 85  Ibs, 

Revolutions  pormta. .J*. 

Indicated  Horse  Power  of  Gas  Cylinder,  804 


FlG.    120. 

stroke.  The  diagrams  from  each  show  that  40  horse  power 
was  developed  by  the  steam  engine,  while  35.4  horse  power 
were  needed  to  compress  and  discharge  the  gas  within  the 


240 


Steam  Engine  Indicator 


compressor.     The  difference  between  the  two,  namely  4.6  horse 
power,  represents   the   loss   caused   by   friction,  amounting  to 


SCALE,  80  IBS.  PER  Sq.  IKCB. 


Topendl 


Ga«qylinder_._lfiW 


FlG.    121. 


FIG.  122. 


11.5  per  cent,  of  the  steam  engine  work,  or  13  per  cent,  of  the 
work  accomplished  with  the  gas  cylinder. 


FIG.  123. 

The  mean  effective  pressure  of  the   compressor  diagrams 
Figs.  1 20  and  121  are  computed  in  the  same  manner  as  that  for 


And  Its  Appliances. 


241 


the  steam  cylinder  and  the  power  developed  is  determined  by 
the  same  rule.  As  the  difference  is  but  4.6  horse  power,  it 
demonstrates  that  88.5  per  cent,  of  it  is  made  to  do  useful 
work. 


FIG.  124. 

Figs.  122  to  125  represent  diagrams  from  an  Otto  gas 
engine  with  a  diameter  of  cylinder  of  6^  inches,  and  the  length 
of  stroke  15^  inches.  The  number  of  explosions  per  minute 
being  130,  and  the  number  of  revolutions  per  minute  260. 
Scale  of  the  spring  208. 


FIG.  125. 


The  following  original  diagrams  Figs.  126,  127  and  128 
were  taken  from  a  rated  7  actual  horse  power  Priestman  safety 
oil  engine.  Diameter  of  cylinder  8  inches  by  8  inches  stroke 
making  350  revolutions  per  minute,  the  scale  of  the  spring 


242 


Steam  Engine  Indicator 


.being  100.     These  three  cards  comprise  a  set,  being  full  load, 
half  load,  and  friction  load  with  the  above  data. 


FIG.  127. 


FIG.  128. 

A  computation  of  the  diagram  at  full  load  Fig.  126  shows 
the  engine  to  be  developing  9.41  indicated  horse  power. 

There  are  still  many  places  where  power  cannot  be  ob- 
tained, except  through  some  form  of  heat  engine,  and  where 
steam  is  unsuitable,  and  gas  perhaps  not  available,  the  oil  en- 
gine has  frequently  presented  itself  and  proved  quite  satisfact- 
ory in  all  such  cases. 

It  is  customary  to  consider  oil  and  gas  engines  as  being 
practically  alike;  but  there  is  one  notable  difference,  in  that, 
if  an  oil  engine  is  run  without  load  it  is  very  liable  to  stop. 
This  applies  only  to  that  type  which  has  no  external  ignition 
to  itself,  neither  by  electricity  nor  otherwise,  but  ignites  only 
by  means  of  a  heated  chamber  which  is  kept  to  ignition  tem- 
perature by  the  repeated  explosions  of  the  charges. 


And  Its  Appliances.  243 

In  this  class  of  oil  engine  the  oil  is  injected  by  a  small 
pump  into  what  is  called  the  vaporizer ;  the  Otto  cycle  is 
worked  and  ignition  takes  place  when  the  mixed  change  of  air 
and  vapor  becomes  compressed  in  the  hot  vaporizer,  the  tem- 
perature of  which  is  kept  up  to  redness. 

In  starting  these  engines  the  vaporizer  is  first  heated  by  a 
lamp  blown  by  a  fan,  or  by  a  retort  blown  by  its  own  self -gen- 
erated oil  gas.  After  being  once  heated  the  vaporizer  is  kept 
hot  by  the  recurring  explosions.  With  a  light  load  there  are 
necessarily  many  explosive  strokes  cut  out  by  the  governor, 
the  same  as  in  case  of  the  gas  engine.  This  so  reduces  the 
generation  of  heat  in  the  cylinder,  that  the  vaporizer  is  not 
maintained  hot  enough  to  ignite  the  vaporized  oil  and  the 
motive  power  is  not  produced,  and  consequently  the  engine 
stops.  From  this  it  is  clear  that  the  size  of  an  oil  engine  must 
correspond  fairly  close  with  the  load  to  be  driven,  or  else  the 
number  of  idle  strokes  will  be  such,  as  to  prevent  the  main- 
tainance  of  a  sufficient  temperature  in  the  vaporizer  to  ignite 
the  charge. 


244  Steam  Engine  Indicator 


CHAPTER  XXX. 


MAKING    CALORIMETER   TESTS. 


When  testing  engines  to  determine  their  economy,  careful 
tests  should  be  made  of  the  quality  of  the  steam  entering  the 
engine,  as  in  many  cases  water  is  carried  over  from  the  boilers, 
and  condensation  in  the  steam  pipes  also  adds  to  the  amount. 

The  priming  of  boilers  is  a  serious  loss  in  many  steam 
plants,  and  for  the  lack  of  proper  appliances  for  determining 
the  same,  it  goes  on  unchecked,  and  often  unknown. 

A  large  proportion  of  the  loss  from  the  priming  of  boilers 
can  be  prevented  if  proper  precautions  be  adopted,  and  thereby 
a  saving  of  coal  effected. 

Long  steam  pipes  also  invariably  cause  condensation,  and 
it  is  very  essential  that  none  of  this  water  should  pass  into  the 
engine,  as  it  occasions  a  serious  loss  by  promoting  initial  con- 
densation in  the  cylinder ;  therefore,  an  efficient  water  separator 
should  be  placed  in  the  steam,  pipe  near  the  engine  in  order  to 
remove  the  water  of  condensation  (as  near  as  possible,)  from 
the  steam, 

The  Calorimeters  that  are  being  used  at  the  present  time, 
are  of  three  kinds,  namely :  The  condensing  or  barrel  calor- 
imeter, the  throttling  or  superheating,  and  the  wire-drawing. 

In  the  first  of  these,  a  certain  weight  of  cold  water  is 
utilized  to  condense  a  certain  weight  of  steam,  and  its  temper- 
ature is  raised  by  the  heat  in  the  steam  to  a  certain  higher 


And  Its  Appliances.  245 

temperature,  depending  upon  the  amount  of  moisture  in  the 
sample  of  steam  condensed.  With  a  device  of  this  kind,  (a 
primitive  form,)  the  appliances  for  determining-  the  weight, 
and  the  temperature  must  be  very  sensitive,  and  the  readings 
carefully  observed  in  order  that  the  results  may  be  approxi- 
mately accurate. 

In  the  second  mentioned,  (the  throttling  calorimeter,)  the 
quantity  of  heat  is  ascertained,  that  is  requisite  to  evaporate, 
and  also  slightly  superheat  the  moisture  contained  in  the  sam- 
ply  of  steam  tested,  and  depends  upon  the  fact,  that  steam 
which  contains  a  moderate  amount  of  moisture  will  become 
superheated  if  the  pressure  is  reduced  by  throttling,  without 
loss  of  heat. 

This  instrument  is  not  only  easier  to  use,  when  the  amount 
of  moisture  is  not  excessive,  but  the  quantities  are  more  ac- 
curately measured  than  in  some  other  forms  of  calorimeters. 

It  is,  however,  somewhat  limited  in  its  range,  and  the  calcu- 
lations rather  complicated  for  other  than  an  expert. 

The  third  form  of  instrument,  or  wire-drawing  calorimeter, 
operates  also  by  superheating,  but  neither  does  this  instrument 
depend  on  any  exterior  source  of  heat  for  this  purpose,  because 
(as  in  the  former  case,)  steam  containing  a  small  amount  of 
moisture  when  wire-drawn,  becomes  superheated  at  the  lower 
pressure ;  the  amount  of  the  superheat  depending  directly  on 
the  percentage  of  moisture  in  the  steam  previous  to  wire- 
drawing. 

In  this  instrument  the  percentage  of  moisture  may  be  very 
accurately  determined,  but  like  the  throttling  calorimeter,  its 
range  is  also  somewhat  limited,  and  the  calculations  compli- 
cated for  the  ordinary  engineer. 

There  is  still  another  form  of  the  instrument,  which  con- 
sists of  a  wire-drawing  device  and  separator  combined. 

The  steam  first  enters  the  water  separator,  in  which  nearly 
all  of  the  moisture  is  separated  from  the  steam  before  it  passes 
to  the  wire-drawing  device. 


246  Steam  Engine  Indicator 

The  water  which  has  been  separated  from  the  steam  may 
be  drawn  off,  and  weighed  separately,  and  the  remainder  of 
the  moisture  is  determined  by  the  amount  of  superheat  in  the 
steam  after  being  wire-drawn. 

In  all  of  the  above  mentioned  calorimeters,  the  steam  sup- 
ply is  taken  from  the  main  steam  pipe,  by  means  of  a  small 
pipe  which  extends  nearly  across  the  main  pipe,  and  is  perfor- 
ated its  entire  length  in  order  to  obtain  as  nearly  as  possible, 
an  average  sample  of  the  steam  passing  through  the  pipe. 

The  rules,  formulas,  and  directions  for  the  use  of  some  of 
the  modern  forms  of  calorimeters  are  commendable  for  their 
accuracy  and  in  some  cases  simplicity,  but  the  principles  upon 
which  their  operations  are  based,  and  results  obtained,  are  in 
many  cases  beyond  the  comprehension  or  understanding  of  the 
ordinary  engineer  unless  he  is  proficient  in  the  higher  branches 
of  mathematics. 

Probably  no  single  operation  pertaining  to  the  science  of 
steam  engineering  requires  greater  care,  manipulation,  and 
accuracy  in  making  steam  tests  than  in  the  use  of  the  calori- 
meter. Therefore,  it  will  be  the  endeavor  here  to  present  this 
important  subject  in  as  simple  a  manner  as  possible  in  order 
that  engineers  not  sufficiently  versed  in  the  higher  mathematics 
may  obtain  the  benefit  of  the  science  connected  therewith. 

In  testing  a  steam  boiler  for  evaporation  alone,  without 
the  calorimeter  test,  but  little  information  is  gained  so  far  as 
the  efficiency  of  the  boiler  is  concerned ;  because  to  determine 
the  real  efficiency  and  economy  in  a  steam  boiler,  the  quality  of 
the  steam  generated  must  be  ascertained ;  as  well  as  the  quan- 
tity of  water  evaporated  per  pound  of  coal,  or  per  pound  of 
combustible. 

The  principle  cause  of  priming  in  boilers  is  due  to 
a  faulty  construction,  and  without  the  calorimeter  test  the 
faulty  constructed  boiler  may,  if  judged  from  the  amount  of 
water  evaporated,  show  greater  efficiency  than  the  properly 


And  Its  Appliances.  247 

constructed  boiler.  If  a  boiler  on  being  tested  carried  off  a  con- 
siderable amount  of  water  with  the  steam,  it  would  be  unfair 
to  credit  it  with  the  evaporation  of  such  water  into  steam, 
because  it  has  only  supplied  enough  heat  to  the  water  carried 
over  to  the  engine  as  to  raise  it  from  the  temperature  of  the 
feed  water  to  the  boiling  point :  this  quantity  of  heat  being 
only  a  fraction  of  that  required  for  its  evaporation  :  Therefore, 
every  pound  of  surplus  water  carried  off  with  the  steam  takes 
a  correspondingly  amount  of  heat  from  the  boiler,  according  to 
the  quantity  of  surplus  steam  carried  over,  and  without  produc- 
ing an  equivalent  in  work  performed.  The  result  of  priming 
is  also  greatly  detrimental  to  the  performance  of  the  engine 
supplied  with  steam  from  such  a  boiler.  It,  therefore,  becomes 
necessary  with  work  in  which  there  is  to  be  any  degree  of 
accuracy,  to  determine  the  quality  of  the  steam  used,  that  is : 
what  percentage  of  it  is  actually  steam,  and  how  much  of  it  is 
water. 

The  main  object  is  to  obtain  steam  as  dry  as  possible, 
without  superheating  it ;  and  the  boiler  that  will  furnish  such 
steam,  and  perform  the  greatest  amount  in  proportion  to  the 
amount  of  fuel  consumed,  may  usualty  be  considered  the  best 
boiler,  all  other  things  being  equal ;  such  as  proper  setting  of 
boilers,  and  properly  constructed  furnaces,  etc. 

Of  the  devices  here  mentioned,  the  most  available,  simple, 
and  comprehensive  for  the  working  engineer,  is  the  condens- 
ing or  barrel  calorimeter  of  the  primitive  form,  with  which 
almost  any  one  interested  in  the  subject  may  equip  himself  at 
little  expense,  and  gain  a  great  amount  of  information  not 
easily  attainable  by  any  other  means. 

It  consists  of  a  simple  barrel  placed  upon  a  platform  scale 
as  shown  in  Fig.  129.  In  the  figure  A.  represents  the  main 
steam  pipe,  and  shows  how  the  attachment  is  made,  and  B. 
represents  a  standard  (made  suitable  for  the  purpose,)  to  which 
the  calorimeter  pipe  is  secured. 


248 


Steam  Engine  Indicator 


That  part  of  the  pipe  that  is  inside  the  main  steam  pipe 
should  be  of  one-half  inch  gas  pipe,  closed  at  the  end,  and  per- 
forated, as  shown,  with  small  holes  about  one-eighth  inch  in 
diameter. 

To  the  valve  attached  to  the  opposite  end  of  this  pipe  it  is 
\  good  plan  to  have  a  petcock  screwed  into  the  top  for  the  pur- 
pose of  being  opened  after  a  test  has  been  completed,  to  allow 
any  water  that  may  remain  in  the  pipe  between  the  valve  and 
the  barrel,  to  fall  to  the  level  of  the  water  in  the  barrel. 
The  down  pipe  leading  from  the  valve  should  have  a  small 
rubber  hose  attached  to  the  end  of  the  pipe,  as  shown  in  the 
figure,  and  reach  to  within  a  short  distance  of  the  bottom  of 
the  barrel. 


FIG.  129. 

The  lower  end  of  the  hose  should  be  closed,  and  the  hose 
above  that  perforated  laterally  all  around  with  small  holes,  to 
avoid  the  jar  due  to  condensation. 

The  barrel  employed  for  this  purpose  should  be  in  such 
condition  as  to  absorb  as  little  water  as  possible  while  making 
the  test. 

In  platform  scales  where  the  beam  is  graduated  to  one- 
half  pounds  only,  it  is  possible,  if  so  desired,  to  read  to 
one-tenth  or  even  one-twentieth  of  a  pound,  by  employing  in 


And  Its  Appliances  249 

connection  with  the  first  weight  an  additional  movable  weight 
one-tenth  of  the  weight  of  that  of  the  first. 

There  should  be  suspended  in  the  barrel,  (in  any  con- 
venient manner  as  will  be  easily  accessible  for  handling  and 
observation,)  an  accurately  graduated  thermometer,  capable  of 
being  read  to  at  least  one-quarter  of  a  degree. 

The  empty  barrel  should  be  accurately  weighed  and  its 
weight  carefully  noted  ;  after  which  (for  convenient  calculation) 
put  an  even  number  of  pounds  of  water  into  the  barrel,  leaving 
sufficient  room  in  the  top  for  the  desired  amount  of  condensed 
steam. 

Then  set  the  scales  so  that  they  will  balance  after  five  or 
six  per  cent,  more  water  has  been  added  in  the  form  of  con- 
densed steam.  Now  remove  the  hose  from  the  barrel,  open 
the  valve  and  let  the  steam  blow  through  long  enough  to  heat 
the  pipes  thoroughly. 

During  the  time  the  steam  is  blowing  through,  take  the 
temperature  of  the  water  in  the  barrel,  and  carefully  make 
memoranda  of  the  same. 

Shut  the  steam  off,  insert  the  hose  into  the  barrel,  and  again 
turn  the  steam  on,  and  as  the  temperature  increases,  gently 
stir  the  contents  with  a  light  wooden  stick,  in  order  to  insure 
the  mixture  being  of  a  uniform  temperature  at  the  time  the 
thermometer  is  read. 

It  is  not  advisable  to  supply  steam  any  longer  than  to 
raise  the  temperature  of  the  water  in  the  barrel  to  about  no 
degrees,  as  beyond  this  temperature,  radiation  may  take  place 
to  such  an  extent  as  will  complicate  the  tests,  and  also  the  re- 
sults. 

It  is  desirable  to  have  the  water  as  cold  as  possible  to 
begin  with,  as  the  greater  the  amount  of  steam  condensed,  the 
less  will  be  a  given  error  in  determining  its  weight  and  pro- 
portion. 


250  Steam  Engine  Indicator 

In  a  short  time  after  the  steam  is  turned  on.  ascertain  how 
near  the  scale  is  in  balance  again,  by  placing  the  hand  tinder 
the  scale  beam  and  raising  it  gently,  and  as  soon  as  it  is  found 
that  the  scales  are  about  to  balance,  shut  the  steam  off,  open 
the  petcock  and  then  balance  the  scales. 

Then  take  hold  of  the  thermometer  and  stir  it  around 
gently  in  the  water  and  carefully  observe  the  highest  tempera- 
ture reached. 

Make  memoranda  of  the  same,  and  also  note  the  weight  of 
water  in  the  barrel. 

The  pipe  leading  from  the  main  steam  should  be  carefully 
felted  and  thoroughly  heated  previous  to  each  experiment,  by 
wasting  steam  through  it  before  placing  the  hose  into  the  cal- 
orimeter. Suppose  that  360  pounds  to  be  the  original  weight 
of  water  put  into  the  barrel  at  the  beginning  of  the  test ;  the 
water  being  at  a  temperature  of  50  degrees  Fahrinheit. 

Now  suppose  steam  of  100  pounds  guage  pressure,  (equiv- 
alent to  1 1 5  pounds  absolute  pressure)  be  run  into  the  water 
until  the  temperature  is  increased  to  110  degrees  Fah.,  and 
that,  upon  re  weighing  its  weight  has  been  increased  by  20 
pounds ;  this  being  the  amount  of  steam  condensed  in  raising 
its  temperature. 

Referring  to  the  table  No.  9,  on  the  properties  of  water 
at  each  degree  of  temperature  it  will  be  found  that  one  pound 
of  water  at  a  temperature  of  50  degrees  Fahrenheit,  con- 
tains 50.003  heat  units;  and  water  at  a  temperature  of  110 
degrees  Fah.  contains  1 10. 1 10  heat  units  per  pound. 

By  reference  to  the  table  No.  8,  on  the  properties  of  sat- 
uarated  steam  at  different  pressures,  it  will  be  found  that  steam 
at  100  pounds  gauge  pressure,  (corresponding  to  115  pounds 
absolute,)  contains  1216.97  heat  units  per  pound  of  steam. 

Then  we  have : 

360  pounds=  weight  of  water  in  the  barrel  before  adding 
steam. 


A  nd  Its  Appliances.  2  5  I 

5 0.003  =  number  of  heat  units  per  pound  of  water  at  50° 
Fahrenheit  before  adding  steam. 

1 10. 1 1 0=  number  of  heat  units  per  pound  of  water  at  1 10° 
Fahrenheit,  the  temperature  after  adding  steam. 

20  pounds  =  weight  of  condensed  steam  and  water  added 
to  the  water  in  the  barrel. 

380  pounds  —  weight  of  water  in  the  barrel  after  adding 
condensed  steam  and  water. 

1216.9741  =  number  of  heat  units  in  one  pound  of  dry 
steam  at  100.304  pounds  gauge  pressure. 

The  percentage  of  water  in  the  steam  may  then  be  calculated 
by  the  following  Rule  : 

First :  Subtract  the  number  of  pounds  of  water  contained 
in  the  barrel  before  the  condensed  steam  was  added  from  the 
total  number  of  pounds  in  the  barrel  after  the  condensed  steam 
was  added,  and  multiply  the  remainder  by  the  total  heat  units, 
as  shown  by  the  table,  contained  in  one  pound  of  steam  due 
the  pressure  per  square  inch  indicated  by  the  steam  gauge  dur- 
ing the  time  the  test  was  made,  and  the  product  will  give  the 
total  heat  units  that  would  have  been  contained  in  the  steam 
that  has  been  discharged  in  the  barrel  if  the  steam  had  been 
dry. 

Second :  Multiply  the  number  of  heat  units  contained  in 
one  pound  of  the  heated  water  in  the  barrel  by  the  number  of 
pounds  of  such  water,  and  the  product  will  give  the  total 
number  of  heat  units  contained  in  the  heated  water  in  the 
barrel. 

Third :  Multiply  the  number  of  heat  units  contained  in  one 
pound  of  unheated  water  in  the  barrel  by  the  number  of 
pounds  of  that  water,  and  the  product  will  give  the  total  num- 
ber of  heat  units  in  the  unheated  water  in  the  barrel. 

Fourth:  Subtract  the  total  heat  units  in  the  unheated 
water  in  the  barrel  from  the  total  heat  units  contained  in  the 
water  after  being  heated,  and  the  remainder  will  give  the 


252  Steam  Engine  Indicator 

number  of  heat  units  that  have  been  added  by  the  steam  and 
water  discharged  into  the  barrel  from  the  steam  pipe 

Fifth :  Subtract  the  heat  units  that  have  been  added  to  the 
original  water  in  the  barrel,  from  the  total  heat  units  that 
would  have  been  contained  in  the  steam  if  the  steam  had  been 
dry,  and  the  remainder  will  show  the  difference  in  heat  units 
between  dry  steam  and  the  steam  discharged  in  the  barrel. 

Sixth:  Multiply  the  heat  units  as  shown  in  table  No.  8, 
contained  in  one  pound  of  steam  due  the  pressure  per  square 
inch  as  shown  by  the  gauge  during  the  test  by  the  number  of 
pounds  of  steam  and  water  that  have  been  added  to  the  orig- 
inal water  in  the  barrel  and  the  product  will  give  the  total 
number  of  heat  units  that  would  have  been  contained  in  the 
steam  that  has  been  discharged  in  the  barrel  if  the  steam  had 
been  dry. 

Seventh :  Divide  the  difference  in  heat  units  between  dry 
steam,  and  the  steam  discharged  in  the  barrel,  by  the  total 
heat  units  contained  in  the  dry  steam,  and  multiply  the  quo- 
tient by  100,  and  the  product  will  give  the  per  cent,  of  water 
contained  in  the  steam  discharged  into  the  barrel. 

This  rule  may  be  resolved  into  a  formula  from  the  data 
given  as  follows : 

Let  H.  =  total  heat  of  steam  at  observed  pressure=  12  16.97 
heat  units  per  pound. 

Let  h  i.  =  weight  of  water  added  by  heating  with  steam  = 
20  pounds. 

Let  W.  =  weight  of  water  in  the  barrel  before  adding 
steam  =  3^0  pounds. 

Let  w  i.  =  weight  of  water  in  the  barrel  after  adding 
steam=3So  pounds. 

Let  t.  =  total  heat  of  water  per  pound  corresponding  to  in- 
itial temperature  of  water  in  the   barrel   at   50°   Fah.  =  5 
heat  units. 


A  nd  Its  Appliances.  253 

Let  T.  =  total  heat  of  water  per  pound  corresponding  to 
final  temperature  of  water  in  the  barrel  at  1  10°  Fah.=  1  10.  1  10 
heat  units.  , 

Let  E.—  heating  efficiency  of  the  steam  furnished  com- 
pared with  the  saturated  steam  between  the  same  limits  of 
temperature. 

Let  Q.=  quality  of  steam  furnished. 

Then  Q.  =  Hxh  i  —  (Txw  i—tx  w)x  100=2.04+  percent. 

Hxh  i 

Or,  by  figures  as  per  data, 


Q=(i2i6.97X  380—  360)—  (no.  110x380—  50.003X360)  X  100= 

1216.  97  X  20 
2.o4+per  cent  of  water  in  the  steam  discharged  in  the  barrel. 

The  value  of  E  may  be  ascertained  by  the  following  formula  : 
*T"TT   /TV       j_\ 

E=  -  \  —  —  .  —  .9774  heating  efficiency  of  the  steam,  or  by 
h  i  (H  —  T) 

^     360   (110.110—50.003)  - 

fio-ures  E  =  -  —  —  -  -  -  -  ~7==.  9774=  same  result  as  above 
20(1216.97—  1  1  o.  1  1  o) 

in  heating  efficiency. 

If  the  steam  is  superheated  it  will  show  a  greater  number 
of  heat*  units  per  pound  for  a  given  pressure  than  is  contained 
in  the  standard  steam  as  shown  in  table  No.  8. 

The  total  heat  of  steam  at  any  given  pressure  corresponds 
to  a  pressure  of  14.7  pounds  above  the  given  pressure,  or  that, 
as  shown  by  the  steam  gauge. 

This  plan  of  making  such  a  test  is  given  as  being  the  most 
available  and  most  .simple  of  comprehension  to  the  ordinary 
working  engineer.  At  the  same  time  the  greatest  care  and 
vigilance  must  be  observed  throughout  in  order  to  get  fairly 
accurate  results,  as  an  error  of  one-quarter  of  a  pound  in  de- 
termining the  amount  of  steam  condensed,  will  make  a  differ- 
ence in  the  result  of  about  three  per  cent.  Also  an  error  of 
one-half  a  degree  in  temperature  will  make  a  difference  in  the 
result  of  at  least  one  and  one-quarter  per  cent. 


254  Steam  Engine  Indicator 

The  scales  must  be  carefully  standardized,  and  as  sensitive 
as  possible  and  greater  accuracy  may  be  attained  by  secur- 
ing a  pointer  to  the  scale  beam,  and  causing  it  to  coincide  at 
each  reading  with  a  set  mark,  by  means  of  small  weights  of 
known  value  placed  upon  the  platform,  the  reading  being 
corrected  accordingly. 

The  thermometer  also  must  be  accurate  and  delicate;  read- 
ing preferably  (when  possible)  to  tenths  of  a  degree. 

The  end  of  the  supply  pipe  must  be  secured  in  the  main 
pipe  in  such  a  way  as  to  obtain  as  nearly  as  possible  an  average 
sample  of  the  steam  passing  through  the  main  steam  pipe. 

The  contents  of  the  barrel  during  the  test  should  be  stirred 
(as  pre-mentioned)  thoroughly,  to  insure  a  uniform  tempera- 
ture at  the  time  the  thermometer  is  read. 

By  exercising  good  judgment,  and  paying  due  attention 
to  all  these  matters  of  detail,  the  results  should  be  within  two 
per  cent,  of  correct. 

The  use  of  the  barrel  calorimeter  has  in  many  cases,  ho  wever, 
been  superseded  by  the  throttling  calorimeter,  especially 
where  very  expert  tests  are  necessary. 

An  improved  form  of  Separating  Calorimeter,  designed  by 
Prof.  R.  E.  Carpenter,  is  illustrated  in  Fig.  130,  which  has  been 
in  use  in  the  laboratories  of  Sibley  College  and  some  other 
places  for  the  past  several  years. 

The  instrument  may  be  described  as  follows :  It  consists 
of  two  vessels,  one  being  inside  the  other ;  the  outer  vessel 
surrounds  the  interior  one  in  such  a  manner  so  as  to  leave  a 
space  between  them  which  serves  as  a  steam  jacket;  the  in. 
terior  vessel  is  provided  with  a  water  gauge  glass  10,  and  a 
graduated  scale  12.  The  sample  of  steam,  the  quality  of  which 
is  to  be  determined,  is  supplied  through  the  pipe  6,  into  the 
upper  part  of  the  interior  vessel. 

The  water  contained  in  the  steam  is  projected  downward 
into  the  cup  14  together  with  the  steam,  where  the  course  of 


And  Its  Appliances. 


255 


the  steam  and  water  is  changed  through  an  angle  of  nearly  180 
degrees,  which  causes  the  greater  weight  of  water  by  its  inertia 

to  be  thrown  outward 
through  the  meshes  in 
the  cup  and  into  the 
space  3  below  in  the 
inner  chamber. 

The  cup  serves  to 
prevent  the  current  of 
steam  from  taking  up 
any  moisture  which  has 
already  been  thrown  out 
by  the  force  of  inertia. 

The  meshes  in  the 
cup  project  upward  into 
the  inside  of  the  cup,  so 
that  the  water  intercepted  will  drip 
into  the  chamber  3,  while  the  steam 
being  deprived  of  a  portion  of  its 
•4  moisture,  passes  upward  and  enters 
the  top  of  the  outside  chamber. 
From  the  outside  chamber  it  is  dis- 
charged through  an  orifice  8,  in  the 
bottom.  This  orifice  is  of  known 
area,  and  is  much  smaller  than  any 
of  the  other  passages  through  the 
calorimeter,  consequently  the  steam 
in  the  outer  chamber  suffers  no 
sensible  reduction  of  pressure  by 
passing  through  the  instrument. 

The  pressure  being  the  same 
in  both  outer  and  inner  chamber 
the  temperature  also  remains  the 
same ;  therefore  no  loss  by  radiation 


12 


FIG.  130. 


256  Steam  Engine  Indicator 

can  take  place  from  the  inner  chamber  except  that  >.  which 
occurs  from  the  exposed  surface  of  the  gauge  glass.  The 
pressure  in  the  outer  chamber  and  also  the  flow  of  steam  in  a 
given  time  is  shown  by  a  special  graduated  gauge  attached 
to  the  instrument. 

The  outer  circle  on  the  gauge  dial  is  graduated  by  trial, 
and  shows  the  weight  of  steam  discharged  in  ten  minutes  of 
time  at  the  observed  pressure.  The  inner  circle  shows  the 
pressure  of  steam  in  the  outer  chamber. 

By  a  law  known  as  Napiers  law,  the  flow  of  steam  through 
an  orifice  from  a  higher  to  a  lower  pressure  is  in  proportion  to 
the  absolute  steam  pressure,  until  the  lower  pressure  equals  or 
exceeds  .6  of  that  of  the  higher. 

Careful  experiments  to  test  the  correctness  of  this  law  has 
in  all  cases  indicated  its  accuracy. 

The  graduations  of  the  scale  12  attached  to  the  inner 
chamber  show  (when  the  index  is  properly  set),  the  weight  of 
water  in  pounds  and  graduated  by  hundredths  which  has  been 
separated  from  the  steam. 

This  scale  is  graduated  by  actual  calibration,  making  it  as 
nearly  correct  as  possible  for  the  temperature  of  water  cor- 
responding to  a  steam  pressure  of  100  pounds  per  square  inch. 

The  percentage  of  moisture  in  the  steam  is  found  by 
dividing  the  weight  of  water  as  shown  by  the  water  gauge  10, 
and  scale  12,  by  the  sum  of  this  quantity  and  that  shown  on 
the  gauge  9.  The  quality  or  percentage  of  dry  steam  is  ob- 
tained by  dividing  the  difference  of  the  readings  by  their  sum. 

The  total  size  of  the  instrument  is  about  10x2^  inches, 
and  its  weight  about  six  pounds. 


And  Its  Appliances .  257 


CHAPTER  XXXI. 


MISCELLANEOUS    DIAGRAMS. 


The  diagrams  illustrated  in  this  chapter,  some  of  which  rep- 
resent an  excellent  distribution  of  the  steam  throughout  the 
stroke,  while  others  are  quite  the  reverse,  serve  to  indicate  the 
beneficial  results  that  may  be  attained  by  a  proper  use  of  the 
Indicator,  and  also  by  its  use  illustrates  the  progress  made  of 
late  years  in  the  distribution  of  steam  in  all  types  of  engines. 
To  a  skilled  engineer  the  diagram  is* an  index  to  the  steam 
economy  of  an  engine,  as  it  shows  the  action  of  the  steam 
throughout  the  whole  cycle  of  the  pistons  movement. 

It  is  a  record  of  the  steam  from  admission  'co  exhaust,  and  no 
card  can  be  considered  complete  which  does  not  indicate  every 
change  from  the  time  the  steam  enters  the  cylinder,  until  it  is 
discharged  either  into  the  atmosphere,  or  the  condenser. 

In  treating  a  card  from  a  compound  or  multi-cylinder  expan- 
sion engine,  the  combined  area  of  all  the  cards  must  be  consid- 
ered, according  to  the  scale  of  each,  in  order  to  ascertain  the 
total  power  developed,  and  the  cost  of  such  power  must  be 
obtained  from  the  terminal  of  the  low  pressure,  or  last  cylin- 
der, as  it  is  at  this  point  that  the  useful  work  of  the  steam 
stops ;  consequently  from  here  the  cost  must  be  obtained. 

It  is  an  established  fact  that  steam  if  expanded  beyond  a  cer- 
tain limit  in  a  single  cylinder  is  accompanied  by  a  loss  in  econ- 
omy ;  therefore  the  only  way  to  increase  economy  is  by  more 
cylinders  and  greater  expansion ;  hence  our  present  tendency 
is  to  higher  steam  pressures  and  multi-cylinder  engines. 


25*'  Steam  Engine  Indicator 

Fig.  131   represents  a  diagram  taken  from  each  end  of  a 
Fishkill  Corliss  Engine.     Diameter  of  cylinder  20  inches  by  48 


FIG.  131. 

inches  stroke,  revolution's  per  minute  58.     Boiler  gauge  84  Ibs. , 
scale  of  spring  40. 


FIG.  182. 


Fig.  132  was  taken  from  an  automatic  slow  speed  engine. 
Diameter  of  cylinder  20  inches,  dia.  of  rod  3  inches,  stroke 
48  inches  making  63  revolutions  per  minute,  63  Ibs.  boiler 
pressure,  scale  of  spring  32. 


And  Its  Appliances. 


Figs.  133  and  134  were  taken  from  the  same  pair  of  en- 
gines as  the  comparative  diagrams  represented  in  Chapter 
XXIV.,  the  data  of  the  engine  being  the  same  as  there  given. 


FIG.  133. 

In  this  case  the  horse  power  developed  being  greater  than  those 
in  the  previous  chapter. 


FIG.  134. 

The  horse  power  developed  by  the  automatic  Fig.  133, 
being  86.26  while  thr.t  of  the  throttling  engine,  Fig.  134,  is 
87.06.  The  mean  effective  pressure  of  each  is  38  Ibs. 


26o 


Steam  Engine  Indicator 


Figs.  135  and  136  were  taken  from  a  side  by  side  double 
Wheelock  engine,  cylinder  18  in.  X48  in.  stroke,  running  54 
revolutions  per  minute,  boiler  pressure  90  Ibs.,  the  cranks  con- 


FIG.  135. 

nected  at  right  angles  or  quartering.  The  M.  E.  P.  of  Fig.  135 
being  32.2  Ibs.,  and  developing  101.75  horse  power  while  the 
M.  E.  P.  of  Fig.  1 36  is  3 1. 8  and  developing  101.44  horse  power. 


FIG.  136. 


Figs.  137  and  138  are  diagrams  from  a  Ball  &  Wood  com- 
pound, high    pressure   cylinder    13    inches,   and  low  pressure 


And  Its  Appliances. 


261 


cylinder  20^  inches  by  15  inch  stroke,  running  270  revolu- 
tions per  minute,  boiler  pressure  145  Ibs.  Scale  of  H.  P.  cyl. 
80,  and  L.  P.  cyl.  20. 


FIG.  137. 


FIG.  138. 

Figs.  139  and  140  are  diagrams  from  a  14  in.  x  14  In.  Fitch- 
burg  engine,  revolutions  154  per  minute.  Boiler  pressure  75 
Ibs.,  by  gauge.  Scale  60.  Fig.  139  shows  the  condition  of  an 


262 


Steam  Engine  Indicator 


engine  when  the  indicator  was  first  applied.     Fig.  140  shows 
the  improvement  made,  an  increase  of  about  40  per  cent,  in 


FIG.  139. 


FIG.  140. 

mean  effective  pressure.  The  cuts  are  full  size,  and  the  load 
on  the  engine  was  200  incandescent  lamps  of  16  c.  p.,  and  39 
arc  lamps,  nominally  2000  c.  p. 


FIG.  141. 
Fig.  141  are  diagrams  taken  from  both  ends  of  a  13  in.  x  13 


A  nd  Its  Appliances .  263 

in.    Armington  &  Sims  engine,  250  revolutions  per  minute. 
Gauge  pressure  85  Ibs.,  and  scale  50. 


FIG.  142. 


FIG.  143. 

Figs.  142  and  143  are  diagrams  taken  from  a  Watts,  Cam- 
bell    tandem  compound    H.    P.    cylinder   18    inches,   and  low 


264  Steam  Engine  Indicator 

pressure  cylinder  32  inches  by  42  inches,  stroke  running  100 
revolutions  per  minute.  Boiler  pressure  120  Ibs.  Scale  H.  P. 
60,  and  L.  P.  10. 


FIG.  144. 

Figs.  144  and  145  were  taken  from  a  7  in.  x  12  in.  Buckeye 
engine.  The  former  was  taken  as  found  running,  as  per  data 
on  card.  The  latter  was  taken  after  the  proper  equalizing  of 
the  valve  connections  had  been  made. 


FIG.  143. 


Figs.  146  and  147  are  diagrams  from  the  high  pressure 
cylinder  of  a  Providence  tandem  compound  engine,  taken 
before  and  after  adjusting.  Diameter  of  cylinder  12  inches. 


And  Its  Appliances. 


265 


Stroke  22  inches,  revolutions  per  minute  175.     Boiler  pressure 
120  Ibs.     Scale  60. 


FIG.  146. 


The  improvement  in  Fig.  147  consisted  in  advancing  the 
eccentric  on  the  shaft,  and  equalizing  the  valve  connections. 


FIG.  147. 


Figs.  148  and   149  are  diagrams  from  a  Corliss  condensing 
engine,  with  data  affixed  thereto.     The  improvement  in  Fig. 


266 


Steam  Engine   Indicator 


149  consisted  of  the  same  treatment  as  that  given  in  the  two 
preceeding  diagrams. 


FOUND  RUNNIAJG 


Rev.  54 

Initial  Dre^.  63.  " 


lie.  148. 


FIG.  149. 


The  diagrams  Fig.  150  were  taken  from  a  Porter- Allen 
condensing  engine,  13  inches  diameter  of  cylinder,  by  24  in- 
ches stroke,  200  revolutions  per  minute.  Boiler  pressure  80 
Ibs.  Vacuum  20  inches. 


And  Its  Appliances. 


267 


Diagrams,  Fig.  151,  were  taken  from  a  14  x  24  x  14  inches 
Westinghouse  compound  engine,  boiler  pressure  120  Ibs. 
Scale  of  Spring  60. 


FIG.  150. 

Fig.  152  shows  a  pair  of  diagrams  (Photo  reduced  in  size) 
taken  from  a  compound  tandem  jacketed  Corliss  engine. 
Diameter  of  IT.  Pressure  cylinder  16^  inches  and  L.  Pressure 


FIG.  151. 

cylinder  32  inches;   stroke  54  inches,    revolutions  per  minute 
59.     Boiler  pressure  108  Ibs. 


268 


Steam  Engine  Indicator 


These  diagrams  shows  the  action  of  the  steam  while  pass- 
ing through  both  cylinders,  and  it  will  be  observed  that  the 
steam  expanded  from  an  initial  pressure  of  121  Ibs.  to  30  Ibs. 
in  the  first  cylinder,  with  an  additional  expansion  in  the 
second,  or  low  pressure  cylinder  to  8  Ibs.,  thus  giving  a  range 
of  temperature  between  341  deg.  and  182  degrees,  a  change  of 
159  degrees.  It  is  very  evident  that  any  attempt  to  get  the 
same  range  of  expansion  from  a  single  cylinder  as  obtained  in 
this  pair,  would  be  attended  with  serious  loss  from  condensa- 
tion ;  hence,  as  higher  steam  pressures  are  used,  and  the  num- 
ber of  expansions  increased,  more  cylinders  are  added  in  order 


FIG.  152. 

to  keep  the  range  of  temperature  in  each  cylinder  within 
economical  limits.  Triple  and  Quadruple  expansion  engines 
are  simply  the  results  of  high  steam  pressure,  and  more  liberal 
expansion. 

The  engines  from  wnich  these  diagrams  were  taken  belong 
to  the  slow  or  medium  speed  type. 

In  reference  to  indicator  cards  in  general  it  will*  be  seen 
that  in  many  cases  their  lines  do  not  reach  that  degree  of  excel- 
lence as  shown  in  Fig.  152. 

The  fault  is  often  due  to  bad  valve  setting  or  poor  valve 
construction,  and  it  may  sometimes  be  due  to  the  indicator 
itself,  either  of  which  may  cause  the  steam  line  to  be  wavy  from 


And  It  a  Appliances. 


269 


start  to  finish.     The  usual  reason  assigned,   however,   is  the 
presence  of  water,  which  comes  in  such  volume  that  its  inertia 


03L 


B.- 


FIG.  154. 

carries  the  indicator  piston  too  far ,  but  the  chances  are  that  if 
\vater  passes  in  such  quantities  to  the  indicator,  the  engine  will 


270  Steam  Engine  Indicator 

not  escape  some  disaster,  and  as  nothing  unusual  happens  when 
such  cards  are  taken  it  is  fair  to  assume  some  of  these  irregu- 
larities are  due  to  other  causes  than  water;  one  of  which  may 
be  considered,  and  what  appear  to  be  the  most  logical  cause. 

Diagrams  Figs.    153   and    154  were  taken  from  high  speed 
engines,  both  taken  at  a  speed  of  350  revolutions  per  minute. 

The  steam  and  expansion  lines  on  Fig.  153  are  all  that  can 
be  desired;  but  the  lines  of  Fig.  154  are  quite  irregular. 

On  each  diagram  a  circle  is  drawn  to  represent  the  travel 
of  the  crank  pin.  The  element  of  time  must  be  considered, 
and  the  influence  it  has  on  the  indicator  piston,  spring,  and 
pencil  movement.  All  of  the  parts  have  weight,  and  conse- 
quently inertia.  If  the  pencil  movement  is  relatively  slow,  the 
inertia,  or  tendency  to  go  too  far,  is  slight  and  our  diagram  will 
be  comparatively  free  from  wave  lines :  on  the  contrary  where 
the  movement  is  rapid,  or  performed  in  an  unusually  short 
time,  the  inertia  will  be  great  and  a  diagram  with  irregular 
lines  will  be  the  result,  as  shown  in  Fig.  154.  The  valve 
motion  of  an  engine  influences  this  time,  and  in  the  cases  of 
Figs.  153  and  154  there  is  enough  difference  in  the  valve  motion 
to  account  for  all  the  difference  in  the  lines  of  the  diagram. 

By  referring  to  the  diagrams  it  will  be  seen  in  Fig.  1 5  3 
that  the  indicator  piston  begins  its  upward  motion  at  a  point 
marked  A  on  the  exhaust  line :  at  this  time  the  crank  is  at  A 
on  the  circle.  If  the  compression  line  is  followed  it  will  be 
seen  that  when  the  indicator  pencil  arrives  at  the  point  B  it  has 
reached  its  limit  of  upward  travel,  and  the  crank  has  passed  on 
to  its  point  B  through  92  deg.  of  the  circle,  or  more  than  one- 
fourth  of  its  entire  travel. 

Here  then  is  a  high-speed  engine  so  far  as  relative  speed 
is  concerned,  but  an  easy  speed  for  indicating;  because  the 
large  clearance,  and  early  compression  makes  the  movement 
of  the  indicator  so  gradual,  that  severe  inertia  shocks  are  elim- 
inated. 


And  Its  Appliances.  271 

Diagram  Fig.  1 54  is  lettered  the  same  but  there  is  a  decided 
difference  in  the  location  of  the  letters.  In  this  case  compres- 
sion did  not  commence  until  the  stroke  was  nearly  finished, 
and  only  rose  a  few  pounds.  Ninety  per  cent,  of  the  upward 
movement  of  the  indicator  pencil  is  represented  by  a  nearly 
vertical  line,  showing  that  this  motion  occurred  while  the 
crank  was  passing  through  a  very  small  part  of  its  travel,  that 
is,  from  A  to  B  on  the  circle. 

If  the  difference  in  the  spaces  between  the  points  A  and  B 
on  the  two  crank  circles  be  compared  they  will  give  a  fair  idea 
of  the  difference  in  the  velocities  of  the  pencil  movement  when 
these  diagrams  were  taken. 

The  difference  is  the  measure  of  the  disturbance,  and  in 
Fig.  153  will  be  found  all  the  conditions  which  insure  a  smooth 
card,  while  Fig.  154  is  decidedly  the  reverse. 

In  indicator  practice  we  occasionally  get  cards  from  slower 
running  engines  which  show  all  the  irregularities  found  in 
cards  from  high-speed  engines  :  but  an  analysis  of  the  diagram 
will  probably  show  that  the  indicator  has  had  but  little  help 
from  compression,  and  the  steam  admission  was  very  quick. 

Most  of  the  excellent  diagrams  taken  from  high-speed 
engines,  and  published  in  the  catalogues  of  indicator  and  engine 
makers,  are  usually  from  compression  engines ;  that  is,  the  type 
which  has  large  clearance  and  early  compression. 

The- diagram  Fig.  155  is,  from  a  pump-cylinder  scale  40, 
and  the  different  lines  represent  all  that  can  be  desired ;  as  the 
nearest  approach  to  a  rectangle  in  a  pump  diagram,  the  better 
practice  it  represents. 

The  line  A  is  the  atmospheric  line,  and  the  distance  from 
that  to  the  lower  line  represent  the  suction,  which  may  be  more 
or  less,  according  to  the  height  the  water  is  lifted,  and  also  to 
the  freedom  with  which  it  passes  to  the  pump.  The  upper 
line  represents  the  pressure  against  the  plunger  or  piston 
necessary  to  force  the  water  out,  and  this  pressure  is  due,  and 


272  Steam  Engine  Indicator 

proportionate  to  the  height  to  which  the  water  is  forced,  and 
also  to  the  friction  it  encounters  in  passing  from  the  pump. 

Commencing  at  the  right  hand  lower  corner  of  the  dia- 
gram, (the  cylinder  being  full  of  water)  and  the  piston  begins 
to  move,  the  pressure  instantly  rises  to  about  75  pounds  above 
atmosphere,  and  continues  at  a  uniform  pressure  to  the  end  of 
the  stroke,  showing  that  there  was  no  shock  due  to  starting  the 
water-column,  and  that  the  passage  of  the  water  from  the  pump- 


FIG.  155. 

cylinder  was  without  additional  resistance.  If  the  cylinder  is 
not  filled  with  water,  the  line  at  the  right  will  not  be  vertical. 
At  the  commencement  of  the  return  stroke  the  pressure 
instantly  fell  to  8^  pounds  below  atmosphere,  the  degree  of 
vacuum  necessary  to  lift  the  water  The  lower  or  suction- 
line  is  about  as  regular  as  the  upper  or  discharge  line  showing 
with  what  freedom  the  water  passes  through  the  suction-valves. 
Such  a  diagram  as  this  shows  an  absence  of  shock  to  the  pump, 
and  that  a  cylinder  full  of  water  is  discharged  at  each  single 
stroke. 


A  nd  Its  Appliances. 


273 


Fig.  156  is  a  specimen  of  diagram  which,  is  often  taken 
from  pumps,  and  shows  that  enormous  shocks  take  place  to  the 
parts  as  well  as  only  partially  rilling  the  cylinder  with  water. 

This  often  happens  in  practice  under  circumstances,  that 
cannot  always  be  avoided,  but  in  all  cases  our  endeavors  should 
aim  to  have  the  lines  of  a  pump-diagram  that  will  enclose  a 
rectangular  figure,  and  as  such,  it  may  be  assumed  that  the 
operations  of  the  pump  must  be  satisfactory.  If  the  construc- 
tion of  the  pump  is  such  that  tortuous  passages  exist,  causing 
undue  friction  of  the  water  getting  into  or  out  of  the  cylinder 


FIG.  156. 

the  shocks  will  be  greater  at  some  parts  of  the  stroke  than  at 
others,  and  this  will  be  shown  by  corresponding  inclinations  of 
the  suction  and  discharge  lines.  Shocks  and  jars  and  inter- 
mittent action  will  be  shown  by  abrupt  irregularities  in  the  lines 
as  in  Fig.  156. 

Fig.  157  represent  diagrams  taken  from  the  steam  cylinder 
of  a  Marsh  pump  working  on  a  suction  lift  of  24  feet. 

By  means  of  a  deflecting  valve,  the  exhausting  end 
of  the  steam  cylinder  can,  when  desired,  be  placed  in  open 
communication  with  the  suction  chamber  of  the  pump.  The 
effect  of  this  connection  is  to  extend  the  vacuum  existing  in 


2/4  Steam  Engine  Indicator 

the  suction  pipe  to  the  exhaust  side  of  the  steam  piston.  'To 
illustrate  the  value  of  this  device  as  claimed  for  it,  is  the  object 
of  the  above  card. 

The  full  lines  were  traced  with  the  steam  exhausting 
directly  into  the  atmosphere.  The  lever  for  operating  the 
deflecting  valve  was  then  thrown  over,  thereby  turning  the  ex- 
haust steam  into  the  suction,  and  the  indicator  pencil  again 
applied  to  the  same  card,  thus  tracing  the  dotted  outline. 


WITH  FXHAUST  STTAM  OUT. 


WITH  EXHAUST  TURNED  IN. 


SCALE  OF  UP::ING  40. 


VACUUM  LINE  11  POUNDS. 

FIG.  157. 


From  this  it  is  apparent  that  the  steam  represented  by  the 
area  enclosed  between  the  upper  full  line,  and  the  upper  par- 
allel dotted  line  is  just  that  much  gain,  for  every  stroke  of  the 
piston,  (in  this  case  nearly  25  per  cent.),  and  it  will  be  further 
noticeable  that  the  total  area  enclosed  by  the  dotted  lines,  ex- 
ceeds the  figure  enclosed  by  the  full  lines  to  a  considerable 
degree,  consequently,  there  is  more  power  to  perform  the 
work,  with  a  smaller  expenditure  of  force,  and  with  the  labor 
a  constant  factor,  the  speed  of  the  pump  is  increased,  and  a 
greater  amount  of  water  delivered. 


A  nd  Its  Appliances.  275 


CHAPTER    XXXII. 


ENGINE    ECONOMY. 


In  considering  the  matter  of  steam  economy  in  the  engine 
alone,  it  must  be  understood  that  the  Mean  Effective  Pressure  of 
the  steam  acting  against  the  piston  for  a  given  time,  represents 
the  exact  measure  or  exponent  of  the  work  performed  by  the 
engine  in  such  time,  and  is  consequently  an  important  factor 
in  all  calculations  pertaining  to  engine  performance. 

The  Terminal  Pressure,  or  that  pressure  of  steam  which 
would  exist  in  the  cylinder,  provided  the  exhaust  valve  re- 
mained closed  to  the  end  of  the  stroke,  is  the  corresponding 
measure  or  exponent  of  the  consumption  of  steam  or  water  by 
the  engine,  or  the  cost  of  the  po^ver,  .and  is  also  an  indispensable 
factor  in  the  calculation  of  the  diagram. 

But  almost  invariably  in  all  makes  of  engines,  the  exhaust 
valte  opens,  and  releases  the  steam  before  the  piston  reaches 
the  end  of  its  stroke ;  and  in  such  cases  the  Terminal  Pressure 
is  found  by  continuing  the  expansion  curve  in  its  gradually 
descending  direction  (by  hand)  to  the  end  of  the  diagram,  and 
measuring  from  that  point  to  the  vacuum  line  by  the  scale  of 
the  diagram,  as  shown  at  T.  V.,  Fig.  77,  page  159. 

From  the  conclusions  conceded  in  reference  to  the  Mean 
Effective  and  Terminal  Pressures,  it  is  evident  that  the  maxi- 
mum economy  will  result  when  the  mean  effective  pressure  is 
greatest  relatively  to  the  terminal  pressure  ;  therefore  if  by  any 
means  the  former  can  be  increased,  without  a  corresponding 


276  Steam  Engine  Indicator 

increase  in  the  latter,  or  anything  that  will  decrease  the  latter 
without  correspondingly  decreasing  the  former,  must  result  in 
improving  the  economy  of  the  engine. 

In  non-condensing  engines,  therefore  it  would  appear  that 
the  maximum  economy  with  a  given  boiler  pressure  is  theor- 
etically obtained  when  the  full  pressure  is  admitted  to  the  cyl- 
inder and  continued  to  such  point  of  cut-off,  as  that  the  degree 
of  resulting  expansion  may  be  such  that  at  the  end  of  the  stroke, 
the  terminal  pressure  has  fallen  to,  or  nearly  to,  atmospheric 
pressure. 

The  attainment  of  this  economy  in  practice  will  depend 
somewhat  upon  conditions,  and  the  construction  of  the  engine ; 
such  as  possessing  a  free  exhast  for  the  steam,  in  combination 
with  the  least  possible  loss  from  clearance,  friction,  leakage 
and  condensation. 

Hence  under  favorable  conditions  it  is  possible  to  expand 
the  steam  until  there  is  no  more  work  in  it,  and  no  greater 
economy  can  be  expected  with  a  given  initial  pressure  of 
steam ;  unless  by  the  aid  of  a  condenser. 

With  a  given  load,  and  boiler  pressure,  the  best  theoret- 
ical economy  is  obtained,  when  the  cut-off  takes  place  as  early 
in  the  stroke,  as  is  consistent  with  obtaining  the  average  pres- 
sure in  the  cylinder  to  do  the  necessary  work,  and  at  the  same 
time  maintain  the  required  speed  of  engine. 

The  measure  of  the  economy  of  the  engine  alone,  therefore 
is  the  number  of  pounds  of  water  which  passes  through  the 
cylinder  in  the  shape  of  steam  per  hour,  for  each  indicated 
horse  power  developed. 

The  actual  amount  of  water  thus  consumed  appears  in 
three  conditions ;  and  consists  in  part  of  the  steam  that  begins 
to  suffer  condensation  immediately  upon  leaving  the  boiler ; 
due  to  coming  in  contact  with  the  comparatively  cooler  steam 
passages,  and  which  is  further  increased  upon  striking  the  in- 
ternal surfaces  of  the  cylinder ;  part  is  condensed  in  the  act  of 


And  Its  Appliances.  277 

transforming  heat  into  work ;  that  is,  in  giving  motion  to  the 
piston,  and  part  in  that  discharged  from  the  cylinder  as  ex- 
haust steam. 

The  portion  condensed  in  the  act  of  changing  heat  into 
work  is  the  only  one  of  value ;  as  this  quantity  (namely,  that 
exhausted  and  that  whose  heat  is  converted  into  work,)  is  the 
amount  of  water,  or  steam  accounted  for  by  the  indicator,  and 
is  a  measure  of  the  performance  of  an  engine,  and  when  com- 
pared with  the  performance  of  the  best,  it  shows  the  economy 
with  which  the  engine  works. 

The  steam  lost  in  internal  condensation  is  not  at  all 
accounted  for  by  the  indicator.  Hence  the  total  amount  of 
loss  from  this  source  is  really  the  difference  between  the  water 
actually  pumped  into  the  boiler,  and  that  accounted  for  by  the 
indicator. 

Tests.  It  is  a  very  simple  matter  in  testing  a  plant  com- 
prising an  engine  and  boilers,  to  ascertain  the  economy  of  the 
plant,  as  a  iv/wle,  as  there  is  usually  but  little  to  determine 
beyond  the  quantity  of  fuel  consumed,  and  the  horse  power 
developed ;  but  to  ascertain  the  economy  and  the  losses,  aris- 
ing from  each  of  the  various  parts  of  a  plant,  (such  as  the 
engines,  boilers,  heaters,  economizers,  pipes,  etc.),  requires 
close  attention  to  all  the  several  points  to  insure  accurate 
results. 

Where  tests  of  the  latter  kind  are  made  the  following  par- 
ticulars and  data  should  be  recorded : 

First.     The  total  weight  of  water  supplied  to  the  boiler. 

Second.  The  quantity  of  water  drained  -from  the  separ- 
ator, (if  one  be  used)  which  includes  the  water  carried  along 
with  the  steam ;  (known  as  priming  and  for  which  the  boiler 
alone  is  responsible)  also  the  condensation  in  pipes. 

Third.  The  percentage  of  moisture  in  the  steam  that  is 
being  supplied  to  the  engine.  This  may  be  determined  by 


278  Steam  Engine  Indicator 

means  of  what  is  called  a  calorimeter  test,  the  method  of  its 
operation  being  described  in  Chapter  XXX. 

From  these  amounts  the  weight  of  steam  (or  water)  passing 
through  the  engine,  per  hour  may  be  ascertained,  and  dividing 
this  weight  by  the  horse  power  developed  will  give  the  weight 
of  steam  used  per  horse  power  per  hour. 

If  this  amount  is  very  high  it  will  probably  be  due  to 
leakage,  and  if  such  should  be  the  case  it  will  be  detected  more 
quickly  by  this  than  by  any  other  method. 

Fourth.     The  total  weight  of  coal  burned  in  the  furnace. 

If  this  weight  is  small  in  comparison  with  the  weight  of 
water  pumped  into  the  boiler,  showing  a  large  evaporation  per 
pound  of  coal,  it  will  probably  be  found  that  the  boiler  primes. 

If  the  opposite  of  this  is  the  case,  it  may  be  due  to  a  poor 
quality  of  coal,  improper  firing,  poor  draft,  etc.,  either  of 
which  will  cause  the  final  results  to  be  disappointing, 

Fifth,  The  temperature  of  the  feed  water  before  and 
after  passing  through  the  heater ;  this  shows  the  efficiency  of 
the  heater. 

In  a  non-condensing  engine  the  heating  of  the  feed  water 
by  the  exhaust  steam  should  always  be  taken  advantage  of,  as 
in  this  way  a  saving  of  coal  will  be  effected  of  from  10  to  15 
per  cent.,  depending  upon  the  efficiency  of  the  heater  and 
manner  of  connecting. 

To  realize  the  full  economy  from  heating  the  feed  water, 
it  should  not  enter  the  boiler  at  a  temperature  less  than  210  de- 
grees Pah.  and  besides,  at  this  temperature  it  also  obviates  the 
strain  on  the  boiler,  that  arises  from  feeding  cooler  water. 

In  a  condensing  engine  however  there  is  but  little  gain 
from  the  use  of  a  heater  over  that  of  feeding  the  boiler  direct 
from  the  hot-well ;  provided  the  temperature  of  the  hot-well  is 
not  unnecessarily  low ;  excepting  under  circumstances  where 
the  water  used  for  condensing  purposes  is  unfit  for  feeding  the 
boiler  on  account  of  salt,  lime,  and  other  substances  held  in 


A  nd  Its  Appliances.  2  79 

solution,  and  which  causes  such  water  to  be  deleterious  in  its 
action  upon  the  interior  surface  of  the  boiler. 

In  the  latter  case  therefore,  a  slight  economy  may  be  de- 
rived from  the  use  of  a  heater ;  as  by  its  use  the  fresh  water 
selected  for  feeding  the  boiler  may  have  its  temperature  con- 
siderably increased  above  that  of  the  hot- well  while  passing 
through  the  pipes  of  the  heater  on  its  way  to  the  boiler ;  and  a 
somewhat  further  gain  is  effected,  which  consists  in  lessening 
the  amount  of  water  requisite  to  supply  the  condenser ;  due  to 
the  heater  condensing  a  portion  of  the  exhaust  steam  in  its 
passage  through  it. 

In  all  steam  plants  there  is  considerable  loss  of  heat  from 
radiation,  by  the  boiler  and  setting,  and  a  large  percentage  of 
the  fuel  burned  simply  replaces  the  heat  radiated  from  this 
source,  such  heat  being  conveyed  away  by  the  air  passing  over 
them,  without  doing  any  useful  work  in  the  way  of  forming 
steam ;  and  a  further  amount  is  also  wasted  by  the  radiation 
from  the  pipes,  etc.,  between  the  boiler  and  engine,  this  latter 
causing  the  condensation  of  steam  in  the  pipes. 

In  order  to  have  a  test  of  this  description  complete,  it  is 
necessary  that  the  amount  of  these  losses  from  radiation  be 
ascertained,  as  the  heat  radiated  from  the  boiler  and  setting 
should  not  be  charged  against  the  steam  formed ;  the  loss  also 
from  condensation  in  the  pipes  is  an  uncertain  quantity  and 
often  much  larger  than  supposed. 

One  plan  of  ascertaining  the  amount  of  each  of  these 
losses  is,  after  the  engine  has  been  stopped,  to  keep  the  nor- 
mal pressure  of  steam  on  the  boiler  for  several  hours,  taking 
care  to  keep  the  water  in  the  boiler,  (as  near  as  possible,)  at 
the  ordinary  level,  and  the  engine  stop  valve  must  be  tightly 
closed  to  prevent  any  escape  of  steam  or  water  through  it. 

The  amount  of  fuel  burned,  and  also  the  quantity  of  water 
pumped  into  the  boiler  during  this  radiation  test,  should  be 
carefully  weighed,  and  at  the  end  of  the  test  the  water  of 


280  Steam  Engine  Indicator 

condensation  must  be  drained  from  the  engine  steam  pipe,  and 
all  other  pipes  connected  directly  with  the  steam  space  of  the 
boiler,  and  this  total  amount  also  carefully  weighed  and  noted. 

If  during  this  test  it  is  found  that  more  water  has  been 
supplied  to  the  boiler  than  that  collected  from  the  drains,  the 
difference  is  evidently  due  to  leakage ;  therefore,  when  taking 
account  of  the  steam  passing  through  the  engine  in  a  power 
test,  this  leakage  should  be  allowed  for. 

Hence,  to  ascertain  the  exact  evaporation  per  pound  of 
coal,  it  is  necessary  that  the  amount  of  coal  burned,  and  water 
used  per  hour  during  the  radiation  test,  be  deducted  from  the 
coal  and  water  used  per  hour  during  the  power  test. 

The  difference  in  the  amount  of  coal,  shown  by  this  sub- 
traction, is  the  actual  amount  that  is  consumed  informing  steam 
only;  while  the  difference  in  the  amount  of  water  used,  shows 
the  exact  amount  of  water  that  has  been  formed  into  steam  by 
this  quantity  of  coal. 

Therefore,  in  power  tests  where  the  amount  of  coal  con- 
sumed is  the  measure  of  the  engine's  performance,  (as  is  fre- 
quently the  case,)  the  quantity  of  coal  remaining  (after  deduct- 
ing the  amount  used  in  the  radiation  test,)  is  the  correct  amount 
chargeable  against  the  engine. 

In  making  the  radiation  test,  every  precaution  should  be 
taken  that  will  tend  to  burn  the  coal  to  the  best  advantage ;  the 
draft  openings  for  the  furnace,  and  also  the  back  damper, 
should  be  carefully  adjusted,  so  as  to  just  maintain  the  pres- 
sure of  steam  required,  and  also  to  prevent  an  excess  of  air 
from  conveying  any  large  amount  of  heat  up  the  chimney. 

In  the  absence  of  an  accurate  water  metre  for  measuring 
the  quantity  of  water  forced  into  the  boiler  during  a  test,  a 
very  satisfactory  arrangement  may  be  substituted,  consisting 
of  two  barrels  or  casks,  in  connection  with  an  ordinary  plat-, 
form  weighing  scales. 


A  nd  Its  Appliances.  2  8 1 

One  of  these  barrels  is  placed  upon  scales,  and  together 
elevated  above  the  second  barrel,  which  for  convenience, 
should  be  somewhat  the  larger. 

The  feed  water  is  drawn  into  and  carefully  weighed  in  the 
upper  barrel,  and  then  run  off  into  the  lower  one,  from  which 
it  is  pumped  into  the  boiler. 

Another  and  somewhat  more  convenient  method  of  testing 
is  sometimes  resorted  to,  but  which  gives  approximate  results 
only.  In  this  operation  the  feed  water  is  brought  to  a  given 
point  near  the  upper  part  of  the  gauge  glass,  and  then  shut  off, 
and  the  test-  made  by  observing  the  rate  at  which  the  water 
boils  away. 

The  height  of  the  water  in  the  glass  at  the  beginning,  and 
at  the  end  of  the  test  being  carefully  observed  and  noted. 

The  weight  of  the  water  evaporated  and  supplied  to  the 
engine  can  then  be  calculated  from  the  cubical  volume  that  it 
occupied  in  the  boiler,  always  bearing  in  mind  that  the  weight 
of  a  given  volume  of  water  varies  with  its  temperature.  (See 
table  No  9). 

To  insure  greater  accuracy,  tests  made  by  this  method  can 
be  repeated  a  number  of  times,  and  the  results  averaged. 

Feed  water  tests,  made  by  measuring  all  of  the  water  sup- 
plied to  the  boiler,  are  of  no  positive  value  unless  leakage  of 
water  from  the  boiler  (if  any  exist)  be  deducted  therefrom ; 
hence,  particular  attention  should  always  be  given  to  this  fact, 
and  the  leakage  determined  as  before  described. 

A  better  and  more  accurate  way  than  either  of  the  above 
methods  for  ascertaining  the  weight  of  steam  consumed  by  an  en- 
gine, is  to  use  a  Surface  Condenser,  in  which  all  of  the  steam 
passing  through  the  engine  is  condensed,  and  the  resulting 
water  saved  and  weighed ;  and  the  only  correction  needed  is 
to  deduct  the  per  cent,  of  moisture  contained  in  the  steam 
supplied,  which  may  be  determined  by  a  Calorimetric  test. 


282  Steam  Engine  Indicator 

A  portion  of  the  steam  required  by  an  engine  may  also  be 
found  by  calculation  from  the  diagram. 

A  method  of  making  this  calculation  is  given  in  Chapter 
XXI. 

Engine  economy  includes  everything  that  enters  into  cost 
of  maintenance,  and  operation,  and  the  problem  with  the  en- 
gineer in  charge  of  engines  and  boilers,  is  how  to  get  the  best 
possible  results  from  such  machinery  as  comes  under  his  direc- 
tion. 

The  value  of  his  services  depends  largely  upon  his  ability 
in  this  direction,  and  an  important  part  of  his  education  is 
how  best  to  accomplish  the  most  desired  and  economical  re- 
sults. 

Economy  to  him  consists  in  keeping  the  fuel  account  as 
low  as  possible  for  the  power  developed,  having  few  repairs, 
little  loss  (through  accidents  or  otherwise)  from  stoppages,  and 
also  having  the  least  possible  loss  from  wear  and  tear  or  de- 
terioration. 

The  cost  of  fuel  is  always  an  important  matter,  but  some- 
times it  happens  of  more  importance  that  there  be  no  com- 
pulsory stoppage  of  the  engine  or  that  the  speed  be  very 
regular. 

It  is  the  province  of  the  engineer  to  study  this  in  any  par- 
ticular instance  and  govern  himself  according  to  circumstances 
and  observation,  and  take  measures  to  obviate  or  remove  (if 
possible)  whatever  may  be  detrimental  to  good  economy. 

In  reference  to  fuel  economy  it  frequently  happens  that 
the  engineer  has  to  contend  with  defective  conditions,  or  under 
such  adverse  circumstances,  as  will,  render  the  attainment  of 
good  economy  impossible. 

A  condition  very  unfavorable  to  fuel  economy  of  non -con- 
densing engines  exists  in  cases  where  the  expansion  line  of 
the  indicator  diagram  falls  below  the  pressure  of  the  atmos- 
phere early  in  the  stroke  (as  shown  in  Fig.  62).  or  in  other 


A  nd  Its  Appliances .  283 

words,  where  the  engine  is  too  large  for  its  work,  necessitating 
an  early  cut-off,  and  in  consequence,  greater  loss  from  con- 
densation. 

The  reason  of  this  increased  loss  through  condensation, 
is  owing  to  the  interior  walls  of  the  cylinder  becoming  cooled 
to  a  lower  temperature  during  expansion  and  exhaust,  and  in 
consequence,  a  considerable  portion  of  the  entering  steam  at 
the  beginning  of  the  stroke  is  condensed  ;  due  to  parting  with 
its  latent  heat  in  order  to  restore  the  temperature  of  the  in- 
terior exposed  surface  of  the  cylinder. 

In  an  engine  with  a  light  load,  the  steam  thus  condensed 
is  a  larger  proportion  of  the  total  steam  used,  than  in  one  more 
heavily  loaded.  Another  reason  why  poor  economy  is  gener- 
ally the  rule  where  light  loads  prevail,  is  that  a  part  of  the 
work  done  in  the  cylinder  of  a  steam  engine  is  in  overcoming 
the  friction  of  the  moving  parts;  and  this  friction  docs  not  in- 
crease proportionately  fast  as  the  load  is  increased,  the  friction 
sometimes  being  nearly  as  great  with  light  running,  or  no 
load,  as  with  the  engine  fairly  well  loaded. 

In  a  non-condensing  engine  the  useless  work  of  moving 
the  piston  against  the  pressure  of  the  atmosphere  must  always 
be  done,  besides  some  additional  back  pressure,  although  this 
will  not  increase  as  fast  in  proportion  as  the  mean  effective 
pressure  is  increased.  In  a  condensing  engine  the  piston  has 
always  to  be  moved  against  pressure  due  to  imperfect  vacuum, 
besides  a  certain  amount  of  back  pressure  also.  Owing  to 
various  conditions  and  circumstances,  connected  with  the  sub- 
ject, the  exact  loss  from  condensation  cannot  be  ascertained 
very  closely  by  calculation;  therefore  it  cannot  be  told  just 
what  the  mean  effective  pressure  on  an  engine  piston  should  be, 
to  realize  the  best  economy  in  fuel  consumption. 

Experiments  to  determine  the  relation  of  steam  consump- 
tion to  point  of  cut-off,  under  different  pressures  of  steam  in  a 
non-condensing  engine  will  be  found  described  in  Chapter  XXVI. 


284  Steam  Engine  Indicator 


CHAPTER  XXXIII. 


The  following  table  (No.  6)  apply  both  to  exhaust  steam 
heaters  and  economizers  where,  what  would  otherwise  be,  waste 
heat  is  utilized  for  heating  the  feed  water. 

The  percentage  of  saving  given  is  the  saving  in  the  amount 
of  heat  required  to  generate  a  certain  quantity  of  steam.  The 
saving  in  fuel  depends  on  other  conditions,  and  may  be  more 
than  given  above.  If,  for  instance,  a  boiler  is  too  small  to 
steam  easily  without  a  feed-water  heater,  the  application  of  a 
heater  will  make  a  much  greater  saving  in  fuel  than  the  per- 
centage given  in  the  table  :  but  if  the  boiler  steams  easily  with- 
out a  heater,  the  addition  of  a  heater  will  save  about  the  same 
per  cent,  of  fuel  as  given  in  the  tables.  It  is  assumed  in  each 
case  that  the  addition  of  an  exhaust  steam  heater  does  not  im- 
pair the  vacuum  on  a  condensing  engine,  or  increase  the  back 
pressure  on  a  non-condensing  engine,  and  that  the  addition  of 
an  economizer  does  not  impede  the  draught. 

A  heater  may  be  applied  to  the  exhaust  pipe  of  a  condensing 
engine  that  will,  without  impairing  the  vacuum,  heat  the  feed-- 
water from  the  temperature  of  the  hot  well  (about  100°)  to  165°  or 
170°,  a  saving  of  about  6  per  cent.,  then  passing  it  through  an 
economizer,  should  raise  the  temperature  another  100°  (from 
170°  to  270°),  making  a  further  saving  of  about  10  per  cent. 

In  non-condensing  engines  an  exhaust  steam  heater  will 
heat  the  feed-water  from  62°  to  210°,  a  saving  of  12.9  per  cent. 

An  economizer  will  heat  the  feed-water  to  from  220°  to 
320°,  according  to  the  temperature  of  the  waste  gases,  and  also 
the  temperature  of  the  water  entering  the  economizer. 


A  nd  Its  Appliances .  285 

After  heating  the  water,  care  should  be  taken  that  it  stays 
hot  until  it  enters  the  boiler.  If,  for  instance,  the  water  is 
heated  in  an  economizer  to  270°,  and  ,then  in  passing  through 
the  pipes  to  the  boiler  it  cools  down  10°,  to  260°,  there  is  a  loss 
of  i. 06  per  cent.,  the  greater  portion  of  which  might  be  saved 
by  carefully  protecting  the  pipes. 

The  temperature  of  the  feed  water,  before  and  after  passing 
through  the  economizer,  and  the  temperature  of  the  gases 
both  sides  of  it,  will  show  whether  the  economizer  is  efficient 
or  not.  If  the  temperature  of  the  water  leaving  the  economizer 
gradually  lowers  while  the  average  temperature  of  the  escap- 
ing gases  gradually  increases,  it  indicates  a  scaling  up  of  the 
economizer,  which  at  once  requires  attention.  Also  if  the 
quantity  of  fuel  increases  gradually,  it  may  possibly  be  due  to 
air  leaks  in  the  setting  or  scaling  either  in  the  boiler,  or  econ- 
omizer, and  should  be  remedied. 


286 


Steam  Engine  Indicator 


TABLE  No.  6. 


Saving  effected  by  the  use  of  Feed-Water  Heaters  in  the  generation  of  steam  of  100  Ibs.  guagt 
pressure  or  115  Ibs.  total  pressure. 


Temp, 
from 
which  the 
water  is 
heated 
or  cooled. 

Temperature  of  the  Water  entering  Boiler. 

32°  |  35°    |   *0°  |   45°   )   50°       53°  |    60"  |    62°  |    63'  |    70°  |    73°       80°  |   88"' 

Percentage  of  gain  (-H  or  loss  (—  )  by  heating  or  cooling  the  water. 

32° 

00 

•25 

•67 

1-10 

1-52 

1-94 

2-36 

2-53 

+ 
279 

+ 
3-21 

H- 

3-63 

+ 
4-05 

+ 
4-47 

35 

-•25 

•00 

•42 

•85 

1-27 

1-69 

2-12 

2-29 

2-54 

2-96 

3-39 

3-81 

4-23 

40 

•67 

-•42 

•00 

•43 

•85 

1-28 

1-70 

1-87 

2<13 

2-55 

2:98 

3-40 

3-83 

45 

1-10 

•85 

-•43 

•00 

•43 

•85 

1-28 

145 

171 

2-13 

2-56 

2-99 

3-41 

50 

1-52 

1-27 

•85 

—  •43 

•00 

•43 

•86 

1-03 

1-29 

1-71 

2-14 

2-57 

3-00 

55 

1-94 

1-69 

1-28 

•85 

-•43 

•00 

•43 

•60 

•86 

1-29 

1-72 

2-15 

2-58 

60 

2-36 

212 

1-70 

1-28 

-86 

-•43 

•00 

•17 

•43 

•86 

1-30 

1-73 

2-16 

62 

2'53 

2'29 

1-87 

1-45 

1-03 

•60 

-•17 

•00 

•26 

•69 

1-13 

1-56 

199 

65 

279 

2-54 

2-13 

171 

1-29 

•86 

•43 

-•26 

•00 

•43 

•87 

1-30 

1-74 

70 

3-21 

2-96 

2'55 

2-13 

1-71 

1-29 

•86 

•69 

-•43 

•00 

•44 

•87 

1-31 

75 

3-63 

3-39 

2-98 

2-56 

2-14 

1-72 

130 

1-13 

•87 

-•44 

•00 

•44 

•88 

80 

4-05 

3-81 

3-40 

2-99 

2-57 

2-15 

1-73 

1-56 

1-30 

•87 

-•44 

•00 

•44 

85 

4-47 

4-23 

3-83 

3-41 

3-00 

2-58 

2-16 

1-99 

174 

1-31 

88 

-•44 

•00 

90 

4'90 

4-66 

4-26 

3-85 

3-44 

3-02 

2-60 

2-43 

2-18 

175 

1-32 

•89 

-•45 

95 

5-33 

5-09 

4-68 

4-28 

3-87 

3-45 

3-04 

2-87 

2-61 

2-19 

176 

1-33 

•89 

100 

575 

5-51 

5-11 

4-70 

4-30 

3-88 

3-47 

3-30 

3*05 

2-63 

2-20 

177 

1-33 

110 

6-59 

6-36 

5-96 

556 

5-15 

474 

4-33 

4-17 

3-92 

3'50 

3-07 

2-65 

2-22 

120 

7-44 

7-20 

6-81 

6-41 

6-01 

5-60 

5-20 

5-03 

4-79 

4-37 

3-95 

3-53 

310 

130 

8-29 

8-06 

7-67 

7-27 

6-88 

6-47 

6-07 

5-91 

5-66 

5'25 

4-34 

4-42 

4-00 

140 

914 

8-80 

8-52 

8-13 

773 

7-33 

6-93 

6-77 

6-53 

6-12 

571 

5-30 

4-88 

150 

9'99 

9-76 

9-38 

899 

8-60 

8-20 

7-81 

7-65 

7-41 

7-00 

6-60 

619 

5-77 

160 

10-84 

10-61 

10-23 

9-85 

9-46 

9-07 

8-68 

8-52 

8-29 

7-89 

748 

707 

6-66 

170 

11-68 

11-46 

11-08 

10-70 

10-32 

9-93 

9-55 

9-39 

9-15 

8-76 

8-36 

7-95 

755 

180 

12-54 

12-31'H94 

11-57 

11-19 

10-80 

1042 

10-26 

10-03 

9-64 

9-24 

8-84 

8-44 

190 

13-39 

13-17  12-80 

12-43 

12-05 

11-67 

11-29 

11-14 

10-91 

10-52 

10-13 

9-73 

9-33 

200 

14-24 

14-02  13-66 

13-29 

12-92 

12-54 

12-17 

12-01 

1179 

11-40 

11-01 

10-62 

10-23 

210 

15'10 

14-89 

14-53 

14-16 

13-79 

13-42 

13-05 

12-90 

12-67 

12-29 

ri-9i 

1152 

1113 

212 
220 

15-27 
15-96 

15-06 
15-74 

14-69 
15-38 

14  33  13-96 
15-02  14-66 

13-59 
14-29 

13-22 
13-92 

13-07 
13-77 

12-85 
1355 

12-47 
13-17 

12-08 
12-79 

11-69 
12-41 

1130 
12-02 

230 

16-81 

16-60 

16-24 

15-89 

15-52 

15-16 

14-79 

14-65 

14-42 

14*05 

13-68 

1330 

1291 

240 

17-66 

17-45 

17-10 

16-75 

16-39 

16-03 

15-67 

15-52 

15-30 

14-93 

14-56 

14-18 

13-81 

250 

18-52 

18-32 

17-97 

17-62 

17-26 

16-91 

1655 

16-41 

16-J9 

1582 

15-45 

15-08 

1471 

260 

19-38 

19-18 

1883 

1849 

18-14 

1778 

17-43 

17^29 

170; 

16-71 

16-35 

15-98 

15-61 

270 

20-24 

20-03 

1969 

19-35 

19-01 

1866 

18-31 

18-17 

1795 

1759 

17-23 

16-87 

16-50 

280 

21-09 

20-89 

20-55 

20-21 

19-87 

19-52 

19-18 

19-04 

ia-83 

18-47 

18-121776 

17-39 

290 

21-95 

2175 

21-42 

21-08 

20-75 

20-40 

20-06 

19-9219-71 

19-36 

19-01  18-65 

18'30 

300 

22-80 

22-61 

22-28 

21-95 

21-61 

21-27 

20-93 

20-80;20'59 

2025 

19-  JO 

19-54 

19-19 

310 
820 

23-67 
24-52 

23-47 
2432 

23-14  22-82 
24-00  23-68 

22-49 
23-35 

22-15 
23-02 

21-82 
22-69 

21-68  21  48 
225622-35 

21  14 
22'02 

20-79  20-44 
21-67121-33 

20-09 
20-98 

And  Its  Appliances, 
TABLE  No.  6.—  CONTINUED. 


287 


Saving  effected  by  the  use  of  Feed- Water  Heaters  in  the  generation  of  steam  of  100  Ibs.  guige 
pressure  or  115  Ibs.  total  pressure. 


Temp, 
from 
which  the 
water  is 
heated 
or  cooled. 

Temperature  of  the  Water  entering  BoMer. 

90°  |    98°  |  100°  |  110"  |  120"  |  130°     140°     180"  |  160°  |  170°,  |  180°     190°     200° 

Percentaee  of  gain  (  +)  or  loss  (—  )  by  heating  or  cooling  the  water. 

32° 

4-90 

533 

5-75 

6-59 

7-44 

8-29 

9-14 

9-99 

10:84 

11-68 

1254 

13-39 

14-24 

35 

4-66 

5-09 

551 

6-36 

7-20 

8-06 

8'80 

976 

10-61 

11-46 

12-31 

1317 

14*02 

40 

4-26 

4-68 

5-11 

5-96 

6-81 

7-67 

8'52 

9-38 

10-23 

11-08 

1194 

12-80 

13-66 

45 

3-85 

4-28 

4-70 

5-56 

6-41 

7-27 

8-13 

8-99 

9-85 

10-70 

1157 

1243 

1329 

50 

3-44 

387 

4-30 

5-15 

6-01 

6-88 

773 

8-60 

9-46 

10-32 

1119 

1205 

12-92 

55 

3-02 

3-45 

3-88 

4-74 

5-60 

6-47 

7-33 

8'20 

9-07 

9-93 

10-80 

1167 

12-54 

60 

2-60 

3-04 

3-47 

4-33 

5-20 

6-07 

6'93 

7-81 

8-68 

9-55 

1042 

1129 

12-17 

62 

2-43 

2-87 

3-30 

417 

5-03 

5-91 

677 

7-65 

8-52 

9-39 

10-26 

11-14 

12.01 

65 

2-18 

2-61 

305 

3-92 

4-79 

5-66 

6-53 

7-41 

8'29 

9-15 

1003 

10-91 

1179 

70 

175 

2-19 

2-63 

3-50 

4-37 

5'25 

6-12 

7-00 

7'89 

8-76 

9-64 

10-52 

11-40 

75 

132 

176 

2-20 

3-07 

3-95 

4-84 

571 

6-60 

7-48 

8-36 

9-24 

10-13 

11-01 

80 

•89 

1  33 

1-77 

2-65 

353 

4-42 

5-30 

6-19 

7-07 

7-95 

884 

9-73 

10-62 

85 

•45 

•89 

133 

2-22 

3-10    4-00 

4-88 

577 

6-66 

7-55 

844 

933 

10-23 

90 

•00 

•44 

89 

1-78 

2-66    3-56 

4-45 

5'34 

6-24 

7-13 

802 

8-92 

9-82 

95 

-44 

•00 

45 

134 

2  23,  3-13 

4-02 

4-92 

5-82 

671 

7'62 

.8-52 

9-42 

100 

•89 

-45 

•oo 

•90 

1-79 

2-70 

"3-59 

4-50 

'5-40 

6-30 

7-20 

8-11 

901 

110 

1-78 

134 

-•90 

•00 

•90 

1-82 

272 

3-63 

4-55 

5-45 

6-36 

7-28 

8-19 

120 

2-66 

223 

179 

-•90 

•00 

•92 

1-83 

275 

3'68 

4-59 

5-51 

6-43 

7'35 

130 

3-56 

3-13 

2-70 

182 

-•92 

•00 

•92 

1-85 

2-78 

3-70 

463 

5-56 

649 

140 

4-45 

4-02 

359 

2-72 

1-83 

-•92 

•00 

•94 

1-88 

2-81 

3-74 

468 

5-62 

150 

5-34 

4-92 

4-50 

3-63 

2-75 

1-85 

-•94 

•00 

•95 

1-89 

2-83 

3-78 

473. 

160 

6-24 

5-82 

5-40 

4-55 

3-68 

2-78 

1-88 

-•95 

•00 

•95 

1-90 

2-86 

382 

170 

7-13 

6-71 

6-30 

5-45 

4-59 

3-70 

2-81 

1-89 

-•95 

•oo 

•97 

1-93 

290 

180 

8-02 

7-62 

7'20 

6-36 

5-51 

4-63 

3-74 

2-83 

1-90 

-•97 

•oo 

•97 

1-95 

190 

8-92 

8-52 

811 

7-28 

6-43 

5-56 

•4-68 

3-78 

2-86 

1-93 

-97 

•00 

98 

200 

9-82 

9-42 

9-01 

8-19 

7-35 

6-49 

5:62 

4-73 

3'82 

2-90 

195 

-•98 

•oo 

210 

1072 

10-32 

9-93 

9-14 

8-28 

7-43 

6-57 

5-68 

478 

387 

293 

198 

-1-00 

212 

10-90 

10-51 

10-10 

9-29 

8-46 

7'61 

675 

5'87 

4-97 

406 

313 

2-17 

1-20 

220 

11-62 

1123 

10-83 

10-02 

9-20 

£•36 

7-51 

6-63 

5-74 

4-84 

391 

295 

200 

230 

12-52 

12-13 

1174 

10-94 

10-12 

9-29 

8-44 

7-58 

6-69 

5-80 

4-88 

395 

299 

240 

13-42 

13-03 

12-64 

11-85 

11-04 

10-22 

9-38 

8-52 

7'65 

677 

5-86 

4-93 

3-99 

250 

14-32 

13-94 

1355 

1277 

11-97 

11-16 

10-33 

9-48 

8-62 

774 

6-84 

5-93 

499 

260 

15-22 

14-85 

14-47 

13-69 

12-91 

12-10 

11-28 

10-44 

9-58 

8-72 

7-83 

692 

600 

270 

16-12 

1575 

15-37 

14*61 

1383 

13-03 

12-22 

11-39 

10-54 

9-68 

8-80 

790 

699 

280 

17'02 

16-65 

16-28 

15-52 

1475 

13-96 

13-16 

1233 

11-50 

10-65 

9-78 

8-89 

798 

290 

1792 

1756 

1719 

16-44 

15-68 

14-90 

14-10 

13-29 

12-46 

11-62 

1076 

9-88 

899 

300 

1882 

1846 

18-09  17-36 

16-60 

15-82 

15-04 

14-24 

13-42 

1259 

1174 

1087 

9-98 

310 

1Q73 

19-37 

19-01  18-28 

17-531676 

15-99 

15-19 

14-38 

1357 

1272 

irse 

1099 

320 

2062 

20-27 

19-9119-19 

184517-69 

16-93 

16-14 

15-34 

1453 

13-70 

1285 

119ft 

288  Steam  Engine  Indicator 

TABLE  No.  6. — CONTINUED. 


Saving  effected  by  the  use  of  Feed- Water  Heaters  in  the  generation  of  steam  of  xoc  Ibs.  guage 
pressure  or  115  Ibs.  total  pressure. 


Temp, 
from 
which  the 
water  is 
heated 
or  cooled. 

Temperature  of  the  Water  entering  Boiler. 

210°  |  212°  1  220°     230°     240°  |  250°  |  260°     270°  |  280°     290°  |  300°  |  310°  |  820° 

Percentage  of  gain  (+)  or  lossj(—  )  by  heating  or  cooling  the  water. 

+ 

+ 

+ 

+ 

+       |  + 

+ 

+ 

32° 

1510 

15-27 

15-96 

16-81 

1766 

18-52 

19  38  20-24  21-09 

21-9522-80 

23-67 

24-52 

35 

14-89 

1506 

15-74 

1660 

1745 

18-32 

19  18  20  03  20-89 

21-7522-61 

23-47 

24-32 

40 

1453 

1469 

1538 

1624 

1710 

17-97 

18-83  19  69  20-55 

2142 

22-28 

23-14 

24-00 

45 

1416 

1433 

15-02 

15-89 

1675 

17-62 

18  49  19-35  20  21 

2108 

21-95 

22-82 

23-68 

50 

1379 

1396 

14-66 

1552 

16-39 

1726 

18  14  19  01  19  87 

2075 

21-61 

22-49 

23-35 

65 

1342 

1359 

1429 

15-16 

1603 

16-91 

17-78  18-66  19-52 

20-40 

2127 

22-15 

23-02 

60 

1305 

1322 

1392 

1479 

1567 

16-55 

17-43  18-31'19  18 

2006 

20-93 

2182 

22-69 

62 

12-90 

1307 

13-77 

14-65 

15-52 

1641 

17-29  18-17  19-04 

19-92 

20-80  21-68 

2256 

65 

12-67 

1285 

1355 

1443 

1530 

16-19 

17'07  17-95  18-83 

1971 

205921-48 

2235 

70 

1229 

12-47 

13-17 

14-05 

14-93 

1582 

167l'l7'59  18-47 

1936 

20-252114 

22-02 

75 

1191 

1208 

12-79 

13-68 

14-56 

1545 

16-35  17'23'lS  12 

1901 

19-9020-79 

21-67 

80 

1152 

1169 

12-41 

13-30 

1418 

15-08 

15-9816871776 

1865 

19'54  20-44 

21-33 

85 

11-13 

11:30 

12-02 

1291 

1381 

14-71 

15-6116-50,1739 

18-30 

19-19 

20-09 

20-98 

90 

1072 

10-90 

11-62 

12-52 

13-42 

14:32 

152216-121702 

17-92 

18-82 

1973 

20-62 

95 

10-32 

10-51 

11-23 

12-13 

1303 

13-94 

14-8515  75  16  65 

17-56 

1846 

1937 

20-27 

100 

9-93 

10-10 

10-83 

11-74 

12-64 

13-55 

14-4715-37  16  28 

1719 

18-09 

1901 

1991 

110 

911 

9-29 

10-02 

10-99 

11*85 

12-77 

13-69146115-52 

1644 

17-36 

1828 

19-19 

120 

8-28 

8-46 

9-20 

1012 

11*04 

U-97 

12  9113  83  14-75 

1568 

16-60 

17-53 

18-45 

130 

7-43 

7-61 

8'36 

929 

1022 

11-16 

12-10  13  03  13-96 

14-90 

15-82 

16-76 

17-69 

140 

6-57 

6-75 

7-51 

844 

9-38 

10-33 

11-2812-221316 

1410 

15-04 

15-99 

16-93 

i 

» 

169 

5-68 

5-87 

6-63 

7'58 

8-52 

9-48 

10-44  11-39 

12-33 

1329 

14-24 

15-19 

16-14 

160 

4-78 

497 

5-74 

6-69 

765 

8-62 

9-58,10-54 

1150 

1246 

1342 

14-38 

15-34 

170 

3-87 

4-06 

4-84 

5-80 

6-77 

774 

8-72 

968 

10-65 

11-62 

12^59 

13-57 

14-53 

180 

2-93 

3-13 

3-91 

4-88 

5'86 

684 

7-83 

880 

978 

10-76'1174 

12-72 

13-70 

190 

1-98 

2-17 

295 

3'95 

4-93 

5-93 

6-92 

7-90 

889 

9-88  10-87 

11-86 

12-85 

200 

1-00 

1-20 

2-00 

299 

399 

4-99 

6-00 

699 

7-98 

8-99 

998 

10-99 

11-99 

210 

•00 

•21 

100 

2-01 

301 

403 

5-04 

605 

7-05 

8-06 

907 

10-09 

11-09 

212 

-•21 

•00 

•81 

1-81 

2-92 

384 

4-85 

5-86 

6-87 

7-88 

8-89 

9-91 

1091 

220 

1-00 

-•81 

•00 

I'Ol 

2-03 

3-05 

4-08 

5-09 

6-11 

713 

8-14 

9-17 

10-19 

230 

2-01 

1-81 

-I'Ol 

•00 

1-03 

2-06 

3-10 

4-12 

5-15 

6-18 

7-21 

8-24 

9-27 

240 

3-01 

2-82 

2-03 

-1-03 

•00 

1-05 

2-09 

3-13 

4-16 

5-21 

6-25 

7-29 

8'33 

250 

4-03 

384 

3-05 

2-06 

-1:05 

•00 

1-06 

2-10 

3-15 

4-21 

'525 

6-31 

7-36 

260 

5-04 

4-85 

4-08 

3-10 

2-09 

-1-06 

•00 

1-06 

2-12 

3-18 

4-24 

5-31 

637 

270 

6-05 

586 

5-09 

412 

3-13 

210 

-1-06 

•00 

1-07 

2-15 

3-22 

4-30 

5-37 

280 

7-05 

tf-87 

611 

5-15 

4-16 

3-15 

2-12 

-1-07 

•00 

1-09 

217 

3-25 

4-34 

290 

8-06 

7-88 

7-13 

6-18 

5-21 

4-21 

318 

2-15 

-1-09 

•00 

1-09 

2-20 

3-29 

300 

9-07 

8-89 

8-14 

721 

6-25 

5-25 

4-24 

3'22 

2-17 

-1-09 

•00 

112 

2-22 

310 

10-09 

991 

917 

8-24 

7-29 

631 

531 

4-30 

3'25 

2-20 

-112 

•00 

1-12 

320 

11-09 

1091 

10.19 

927 

833 

736 

637 

5-37 

434 

3-29 

2-22 

-1-12 

•00 

And  Its  Appliances. 


289 


TABLE  No.  7. 

Areas  and  Circumferences  of  Circles  from  i  64  to  4  inches  in  diameter  varying  by  sixteenths* 
a iid  from  4  inches  to  100  inches  varying  by  one-eighth  inch. 


Diam. 
in 
Inches. 

Area 
in  Square 
Inches. 

Circum. 
in 
inches. 

Diam. 
in 
Inches. 

Area 
in  Square 
Inches. 

Circum. 
in 
Inches. 

Diam. 
in- 
Inches. 

Area 
in  Square 
Inches. 

Circum. 
in 
Inches. 

••fc1? 

0.00019 

0.0490 

3 

{9 

7.3662 

9.6211 

8.| 

55-088 

26.31 

X 

0.00076 

0.0951 

.- 

\ 

7.6699 

9-8I75 

.• 

56.745 

26.70 

•• 

s 

0.00306 

0.1963 

. 

r3* 

7.9798 

10.0138 

58.426 

27.10 

L 

0.0122 

0.3927 

•  * 

( 

8.2957 

10.2102 

.; 

60.132 

27.49 

5 

O.O276 

0.5890 

•" 

-V 

8.6179 

10.4065 

61  .862 

27.88 

.1 

0.0490 

0.7854 

.j 

r 

8.9462 

10.6029 

9-. 

63.617 

28.27 

•- 

V 

0.0767 

0.9817 

ft 

9.2806 

10.7992 

•j 

65-396 

28.66 

-1 

-7 

0.1104 

1781 

j 

- 

9.621  1 

10.9956 

67  200 

29.06 

•1 

0.1503 

•  3744 

•' 

-95 

9.9678 

II.I9I9 

-; 

' 

69.029 

29-45 

•i 

f 

0.1963 

.5708 

- 

1 

10.3210 

11.3883 

70.882 

29.85 

•• 

-9* 

0.2485 

.7671 

- 

rg 

10.6796 

11.5846 

•' 

72.759 

30.24 

} 

0.3067 

.9630 

.j 

f 

10.9446 

II.78IO 

•  ; 

74.662 

30.63 

'-] 

-£ 

0.3712 

2.1590 

•• 

6 

II-4I59 

11.9773 

•i 

76.588 

31.02 

' 

0.4417 

2.3565 

*i 

' 

11.7932 

12.1737 

78.540 

31  42 

1 

0.5174 

2-5512 

12.1768 

12  3700 

I0't 

80.515 

31.81 

•f 

• 

0.6013 

2.7490 

4- 

12566 

12.57 

82.516 

32.20 

H 

0.6902 

2-9453 

> 

I3.364 

12.96 

84.540 

32-59 

i. 

0.7854 

3.1416 

'•A 

•  4 

14.186 

I3.35 

86.590 

32.99 

i 

\5        o.S86i 

3-3379 

I5.033 

13.74 

88.664 

33.38 

-i 

0.9940 

3-5343 

15.904 

14.14 

90.762 

33-77 

3C                1075 

3-7306 

16.800 

14-53 

•i 

' 

92.885 

34.16 

•' 

2271 

3.9270 

17.720 

14.92 

n. 

95-033 

34.56 

•i 

55              -3529 

4-1233 

18.665 

J5-32 

•£ 

97  205 

34-95 

•t 

. 

.4848 

4.3197 

5. 

I9.635 

99.402 

35-34 

•i 

.6229 

4.5160 

20.629 

I6.IO 

.. 

101  62 

35  74 

•j 

• 

.7671 

•4.7124 

21.648 

16.49 

j« 

103.87 

36.  13 

9ff. 

•9175 

4.9087 

22.690 

16.89 

106.  14 

36.52 

2.0739 

5-1051 

B 

23.758 

17.28 

.i 

108.43 

3691 

£ 

2.2365 

5-30I4 

24.850 

17.67 

110.75 

37-31 

,j 

2.4052 

5.4978 

25.967 

18.06 

12. 

113.10 

37-70 

.• 

f 

2.5801 

5-6941 

*fc 

27.108 

18.46 

. 

115-47 

38.09 

.- 

2,7611 

5-8905 

6. 

28.374 

18.85 

117.86 

38.48 

f 

2.9483 

6.0868 

1 

29.464 

19.24 

. 

120.28 

38.88 

2. 

3.1416 

6.2832 

• 

30.680 

19.64 

122.72 

39-27 

•1 

-V 

3-34H 

6-4795 

- 

3i-9T9 

20.03 

125.18 

39.66 

•1 

• 

3-5468 

6-6759 

• 

33-183 

20.42 

- 

127.68 

40.06 

3.7582 

6.8722 

• 

34-471- 

20.81 

-1 

130.19 

40.45 

.- 

- 

3.9760 

7.0686 

35.785 

21.21 

13- 

132.73 

40.84 

4.2001 

7.2649 

• 

37.122 

21.  6O 

135-30 

4L23 

.j 

• 

4.4302 

7.4618. 

7- 

38.484 

21.99 

.. 

137-^9 

41.63 

.•j 

4.6664 

7-6576 

.4 

L 

39-871 

22.38' 

140.50 

42.02 

.-1 

• 

4.9087 

7.8540 

41.282 

22.78 

>: 

143-  *4 

42.41 

9J 

5-^573 

8.0503 

p 
' 

42.718 

23.17 

.. 

14580 

42.80 

\ 
'•  i 

5.4II9 

8.2467 

44-179 

j) 

148.49 

43-20 

I 

5.6727 

8.4430 

23-95 

. 

151.20 

43-59 

.; 

5-9395 

8.6394 

47.173 

24-35 

14. 

153-94 

43.98 

.^ 

i 

6.2126 

8-8357 

•i 

. 

48.707 

24-74 

156.70 

44.38 

•i 

6.4918 

9-0321 

s. 

50.265 

25.13 

,| 

I59.48 

44-77 

•   .< 

5 

I 

6.7772 

9.2284 

•i 

51,848 

25.52 

•8 

162.29 

45.16 

3- 

7.0686 

94248 

J 

53456 

25.92 

'* 

165-13 

45-55 

2  go 


Steam 


Engine 


Indicator 


TABLE  No.  7. — CONTINUED. 

Areas  and  Circumferences  of  Circles  from   1-64  to  4  inches  i:i   diameter,  varying  by  sixteenths; 
and  from  4  inches  to  100  inches  varying  by  one-eighth  inch. 


Diam. 
in 
Inches. 

Area 
in  Square 
Inches. 

Circuni. 
in 
Inches. 

Diam. 
in 
Inches. 

Area 
in  Square 
Inches. 

Circuni. 
in 
Inches. 

Diam. 
in 
Inches 

Area 
in  Square 
Inches. 

Circum. 
in 

Inches. 

14  f 

167.99 

45-95 

2I.| 

358.84 

67  15 

284 

621.26 

88.36 

| 

17087 

46.34 

363-05 

67-54 

tl 

626.80 

88.75 

£ 

173.78 

46.73 

•f 

367.28 

67.94 

632.36 

89.14 

15 

176.71 

47-12 

.| 

371-54 

68.33 

.;• 

63794 

89-54 

i 

179.67 

47.52 

•8 

375.83 

68.72 

,\  • 

643-55 

89-93 

1 

182.65 

47  91 

22. 

3SO.I3 

69.12 

.= 

649.18 

90.32 

i 

185.66 

48.30 

•* 

384.46 

69.51 

•i  ' 

654.84 

90.71 

188.69 

48.69 

388.82 

69.90 

29. 

660.52 

91.11 

^ 

I9I-75 

49.09 

393-20 

70.29 

"8 

666.23 

91.50 

1 

194.83 

49.48 

397-61 

70.69 

'T 

671.96 

91.89 

* 

197-93 

49-87 

402.04 

71.08 

•t 

677  71 

92.28 

16 

2or.o6 

50.27" 

,| 

406.49 

71-47 

•i 

683.49 

92.68 

* 

204.22 

50.66 

•3 

410.97 

71.86 

•f 

689.30 

93-°7 

i 

207.39 

51-05 

23. 

415.48 

72.26 

.? 

695.I3 

93-46 

1 

2  10.  60 

51-44 

4 

420. 

72.65 

•a 

700.98 

93-85 

213.82 

51.84 

1 

424-56 

73-04 

30. 

706.86 

94-25 

1 

217.08 

52.23 

429-13 

73-43 

4 

712  76 

94-64 

4 

220.35 

52.62 

•2" 

433-74 

73.83 

'4 

718.69 

95-03 

1 

223.65 

53-oi 

•i 

438.36 

74.22. 

"8 

724.64 

95-43 

17 

226.98 

53-41 

•f 

443-01 

74.6i 

.X 

730.62 

95.82 

1 

230.33 

53-8o 

•W 

447-70 

75- 

•f 

736.62 

96.21 

i 

233.70 

54-19 

24. 

452-39 

75.40 

s 

742.64 

96760 

{ 

237  jo 

54-59 

4 

457  ii 

75-79 

•8 

748.69 

97- 

240.53 

54.98 

_L 
*  4 

461.86 

76.18 

31- 

754-77 

97-39 

£ 

243.98 

55-37 

'! 

466.64 

76.58 

760.87 

9778 

a 

4 

247-45 

55-76 

47L44 

76.97 

.J- 

766.99 

98.17 

1 

250.95 

56.16 

•8 

4/6.26 

77.36 

•t 

773-14 

98.57 

18 

254-47 

56.55 

*  4" 

481.11 

77.75 

'1 

779-31 

98.97 

258.02 

56.94 

•1 

485.98 

78.15 

•f 

785-51 

99-35 

261.59 

57-33 

25- 

490.87 

78.54 

'I 

791-73 

99-75 

265.18 

57-73 

•f 

495.8o 

78.93 

•8 

797.98 

100.14 

268.80 

58.12 

500.74 

79-33 

32. 

804.25 

100.53 

272.45 

58.51 

•I 

505.71 

79.72 

•i 

810.54 

100.92 

276.12 

58.90 

i 

510.71 

80.  1  1 

.JL 

816.86 

101.32 

279.81 

59-30 

•f 

515.72 

80.50 

.j  • 

823.21 

101.71 

19 

283.53 

59-69 

•  4 

520.77 

80.90 

829.58 

102.10 

287.27 

60.08 

•I 

525.84 

81  29 

835.97 

102.49 

291.04 

60.48 

26. 

530.93 

81.68 

842.39 

102.89 

294.83 

60.87 

536.05 

82.07 

848.83 

103.28 

298.65 

61.26 

• 

54LI9 

82.47 

33- 

855-30 

103.67 

302.49 

61.65 

546.36 

82.86 

4 

861.79 

104.06 

-306.35 

62.05 

55L55 

83.25 

4 

868.30 

104.46 

310.25 

62.44 

556.76 

83.64 

•I 

874.84 

104.85 

20 

314.16 

62.83 

•1 

562. 

84.04 

881.41 

105.24 

L 

318.10 

63.22 

'1 

567.27 

84.43 

•8 

888. 

105.64 

.  [• 

322.06 

63-62 

27. 

572.56 

84.82 

•f 

894.62 

106.03 

.  | 

326.05 

64.01 

577.87 

85.21 

fcfl 

901.25 

106.42 

,.t 

330.06 

64.40 

•T 

583-21 

85.61 

34. 

907.92 

106.81 

.  | 

334-10 

64.79 

•f 

588.57 

86. 

*• 

914.61 

107.21 

.  \ 

338.16 

65-19 

•f 

593.96 

86.39 

921.32 

107.60 

.  [ 

342-25 

65-58 

•\ 

599-37 

86.79 

•8 

928.06 

107.99 

21    - 

346.36 

65.97 

.| 

604.81 

87:18 

.1 

934-82 

108.39 

i 

350.50 
354-66 

66.37 
66.76 

28'.  8 

610.27 
615.75 

87.57 
,87,96 

^ 

941.60 
948.42 

108.78 
109.17 

And  Its  Appliances 


291 


TABLE  No.  7. — CONTINUED. 

Areas  and  Circumferences  of  Circles  from   1-64  to  4  inches  in  diameter  varying  by  sixteenths; 
and  from  4    inchrs  to  100  inchts  varying  by  one-eighth  inch. 


Diam. 
in 

Inches. 

Area 
in  Square 
Inches. 

Circum. 
in 
Inches. 

Diam. 
in 

Inches. 

•^    Area 
in  Square 
Inches. 

Circum. 
in 
Inches. 

Diam. 
in 
Inches 

Area 
in  Square 
Inches. 

Circum. 
in 
Inches. 

344 

955-25 

109.56 

4r.S 

1360.8 

130.8 

4S.f 

1837-9 

'52. 

35- 

962.11 

109.96 

•f 

1369- 

131.2 

,4 

I847.5 

152.4 

4 

968.99 

110.35 

•8 

1377-2 

I3I.6 

«f 

1857. 

152.8 

975-91 

110.74 

42. 

I3S5.4 

13^.9 

•I 

1866.5 

153-2 

•f 

982.84 

III  13 

4 

1393-7 

132.3 

•8" 

1  876.  1 

153-5 

. 

989.80 

111-53 

•I 

1402. 

132.7 

49- 

1885.7 

^539 

996.78 

111.92 

i' 

1410.3 

I33-I 

j. 

•8 

1895.4 

154-3 

. 

1003.79 

112.31 

1418.6 

133-5 

.1 

1905. 

154-7 

•£ 

1010.80 

112.70 

1427. 

133-9 

•i 

•1914.7 

I55-I 

36. 

1017.88 

113.10 

1435-4 

134.3 

1924.4 

155-5 

•4 

1024.95 

U3-49 

1443-8 

134.7 

•1 

I934-I 

I5S-9 

>< 

. 

1032.06 

113.88 

43- 

1452.2 

I35-I 

a 

1943-9 

156.3 

1039.19 

114.28 

4 

1460.6 

135-5 

•8 

1953-7 

I56./ 

1046.35 

114.67 

1469.1 

135-9 

50. 

I963-5 

I57-I 

. 

1053.52 

II5.06 

1477-6 

I36.3 

•i 

1973-3 

157-4 

1060.73 

U5-45 

•it 

1486.2 

136.7 

i 

1983.2 

I57.9 

1067.95 

H5.85 

•s 

1494-7 

I37.I 

1993- 

158.2 

37- 

1075.2 

116.2 

•  4 

I503.3 

137-4 

•i 

2003. 

158.7 

4 

1082.5 

116.6 

4 

.1511.9 

137-8 

•f 

2012.8 

J59- 

1089.8 

117. 

44. 

1520.5 

138.2 

.2 

2022.8 

159-4 

1097  1 

117.4 

•i 

1529.2 

138.6 

•« 

2032.8 

159-8 

1104.5 

117.8 

i 

1537-9 

T39- 

5i. 

2042.8 

160.2 

im.S 

IlS.2 

1546.5 

139-4 

i 

2052.8 

160.6 

1119.2 

118.6 

.-} 

1555-3 

139-8 

2062.9 

161. 

•ri' 

1126.7 

119... 

•i 

1564- 

140.2 

•t 

2072.9 

161.3 

33. 

1134.1 

119.4 

.| 

1572.8 

140.6 

•i 

2083.1 

161.8 

4 

1141.6 

119.8 

•8 

1581.6 

141. 

«$ 

2093.2 

162.1 

m. 

. 

1149.1 

120.2 

45- 

1590.4 

141.4 

2. 

2103.3 

162.6 

.j 

1156.6 

120.6 

.J1 

1599-3 

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•i 

2II3-5 

162.9 

.- 

1164.2 

121. 

•4 

1  608.  2 

142.2 

5*. 

2123.7 

163.4 

1171.7 

I2I.3 

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1617. 

142.6 

2133-9 

163-7 

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II79-3 

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1626. 

142.9 

•T 

2144.2 

164.1 

•i 

1186.9 

I22.I 

•f 

1634.9 

143-3 

•f 

2154-4 

164.5 

39- 

1194.6 

122.5 

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"4 

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143-7 

•f 

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164.9 

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1202.3 

122.9 

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1652.9 

144.1 

«t 

2175. 

165.3 

.; 

1  2  10. 

123.3 

46. 

1661.9 

144.5 

•f 

2185.4 

165-7 

.j 

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123.7 

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I67I. 

144.9 

•8 

2195-7 

1  66.  1 

1225.4 

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1680. 

145-3 

53- 

2206.2 

166.5 

.j 

1233.2 

124.5 

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1689.1 

145-7 

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2216.6 

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124.9 

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2227. 

167.3 

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1256.6 

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126.4 

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1734.9 

147.7 

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2269. 

168.9 

,\ 

1280.3 

126.8 

i 

1744.2 

148. 

•1 

2279.6 

169.2 

.; 

1-288.2 

127.2 

1753.5 

148.4 

54- 

2290.2 

1696 

1296.2 

127.6 

•t 

1762.7 

148.8 

2300.8 

170. 

.; 

1304.2 

128. 

»i 

1772.1 

149.2 

.2, 

2311.5 

170.4 

J 

I3I2.2 

128.4 

•t 

1781.4 

149.6 

•i 

2322.1 

170.8 

41. 

1320:3 

I2S.8 

,i 

1790.8 

ISO. 

•f 

2332.8 

171.2 

•& 

1328.3 

129.2 

•8 

1  800.  i 

150.4 

-t 

2343-5 

171.6 

.£ 

1336.4 

129.6 

48. 

1809.6 

150.8 

•4 

2354.3 

1/2. 

•I 

1344-5 

130. 

4 

1819. 

151.2 

•8 

2365 

172-3 

rf 

1352.7 

130.4 

4 

1828.5 

I5I.6 

55. 

2375.8 

172.8 

292 


Steam  Engine  Indicator 


TABLE  No.  7.— CONTINUED. 

Areas  and  Circumferences  of  Circles  from  1-64  to    4  inches  in  diameter  varying  by  sixteenths; 
and  from  4  inches  to  100  inches,  varying  by  one-eighth  inch. 


Piam. 
in 
Inches. 

Area 
in  Square 
Inches. 

Circum. 
in 
Inches. 

Diam 
in 
Inches. 

Area 
in  Square 
Inches. 

Circum. 
in 
Inches. 

Diam. 
in 
Inches 

Area 
in  Square 
Inches. 

Circum. 
in 
Inches: 

55-1 

2386.6 

I73-I 

6f.| 

3006.9 

194-3 

68.| 

3698.7 

215-5 

2397-5 

173-6 

62. 

3019.1 

194-8 

•4 

3712.2 

215-9 

. 

2408.3 

173-9 

.* 

3031.2' 

I95-I 

•i" 

3725.7 

216.3 

2419.2 

174.4 

3 

3043.5 

195-6 

69  . 

3739-3 

216.7 

.: 

2430-  1 

I7J.7 

;i 

3055.7 

195-9 

.i 

3752.8 

2I7.I 

2441- 

I75-I 

•i 

3068. 

'.'96.3 

3766,4 

217.5 

.: 

2452., 

175-5 

•8 

3080.2 

196.7 

3780. 

217.9 

56. 

2463. 

175-9 

,1 

3092.6 

197.1 

3793-7 

218.3 

~~, 

-2474. 

176.3 

•8 

3104.8 

197.5 

3807.3 

218.7 

f', 

2485. 

176.7 

63. 

3117.2 

197.9 

3821. 

219.1 

.'• 

.2496.1 

177.1 

3129.6 

198.3 

3834.7 

219-5 

.• 

2507.2 

177.5 

.1 

3142. 

198.7 

70. 

3848.5 

219.9 

.• 

2518.2 

177.8 

•t 

3154-4 

199. 

.i 

3862.2 

220.3 

,i 

25294 

•178-3 

•^ 

3166.9 

199-5 

•t 

3876. 

22O-7 

.- 

2540-5 

178.6 

•f 

31794 

199.8 

.1 

3889.8 

221. 

57- 

2551.8 

J79-I 

.| 

3i9x-9 

200.3 

•f 

3903-6 

221.5 

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2562.9 

179:4 

•8 

3204.4 

200.6 

.1 

39I7.4 

221.8 

2574-2 

179.9 

64. 

3217- 

2OI.I 

.1 

393L4 

222.2 

25854 

180.2 

3229.5 

201.4 

.1 

3945-2 

222.6 

., 

2596.7 

180.6 

•i 

3242-2 

201.8 

7I', 

3959-2 

223. 

2608. 

181. 

•f 

3254-8 

202.2 

.i 

3973-1 

223.4 

J 

2619.4 

181.4 

•£ 

3267-5 

202.6 

.i 

3987.1 

223.8 

.- 

2630.7 

181.8 

•  $ 

3280.1 

203.      « 

•f 

4001.1 

224.2 

& 

2642  I 

182.2 

a 

3292,8 

203.4 

•i 

4015.2 

224.6 

2653.4 

182=6 

i 

3305.5 

203.8 

.1 

4029.2 

225. 

•¥ 

2664.9 

183. 

65. 

33l8-3 

204.2 

•f 

4043-3 

225.4 

•i 

2676.3 

183-3 

3331- 

204.5 

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4057- 

225.8 

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2687.8 

183.8 

3343-9 

205. 

72. 

407L5 

226.2 

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3356.7 

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4085.6 

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2710.9 

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3369-6 

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4099.8 

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•8 

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184.9 

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3382.4 

206.  1 

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227-3 

59- 

2734- 

185.4 

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206.6 

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4128.2 

227.7 

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3408.2 

206.9 

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2757.2 

186.1 

66. 

3421.2 

207.3 

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228.5 

2768.8 

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3434-1 

207.7 

4 

4171. 

228.9 

.; 

2780.5 

186.9 

I 

34472 

208.  1 

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4185.4 

229.3 

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2792.2 

187.3 

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3460.  i 

208.5 

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3473-2 

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.i 

4214.1 

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2815.6 

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•8 

3486.3 

209.3 

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230.5 

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2827.4 

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2839.2 

188.8 

•f 

3512.5 

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2851. 

189-3 

67- 

3525-6 

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.* 

3538.8 

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232. 

•f 

2874.8 

190.1 

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3552. 

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2898.5 

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.A 

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61. 

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a 

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212.8 

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4-359-2 

234. 

2934.4 

192. 

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213.2 

J 

4373-8 

234-4 

.; 

2946.5 

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68. 

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213.6 

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4388.5 

234-8 

2958.5 

192.8 

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214. 

rl 

4403.1 

235-2 

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2970.6 

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| 

3658-4 

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214.8 

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4432.6 

236. 

•f 

2994.8 

194. 

J 

3685-3 

215.2 

•i 

4447-4 

236.4 

And  Its  Appliances. 


293 


TABLE  No.  7=— CONTINUED. 

Areas  and  Circumferences  of  Circles  from  1-64  104  inches  in  diameter  varying  by  sixteenths; 
and  from  4  inches  to  100  inches,  varying  by  one-eighth  inch. 


Diam. 
in 
Inches. 

Area 

n  Square 
Inches. 

Circum. 
in 
Inches. 

Diam. 
in 
Inches. 

Area 
in  Square 
Inches. 

Circum. 
in 
Inches. 

Diam. 
in 
Inches. 

Area 
n  Square 
Inches. 

Circum. 
in 
Inches. 

75-1 

4462.  1 

236.7 

S2.£ 

5297-I 

258. 

884 

6203.6 

279.2 

4477- 

237.2 

•I 

53I3-3 

258.4 

89. 

6&I.I 

279.6 

*f 

4491.8 

237-5 

4 

53294 

258.8 

*f 

6238.6 

280. 

.1 

4506.7 

238. 

,1 

5345-6 

259.2 

•i 

6256.1 

280.4 

.i 

4521-5 

238.3 

I 

5361.8 

259.6 

a. 

•  8 

6273-6 

280.8 

76. 

4536.5 

238.8 

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5378.1 

260. 

6291.2 

281.2 

4 

4551-4 

239.1 

•i 

5394-3 

260.4 

•il 

6308.8 

281.6 

i 

4566.4 

239-5 

83- 

5410.6, 

260.8 

•  4" 

6326.4 

282. 

•1 

45SI.3 

239-9 

•* 

5426.9 

26l.I 

•1 

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282.3 

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4596-3 

240.3 

4 

5443-3 

261.5 

90. 

6361.7 

282.7 

•s 

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;» 

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5459-6 

261.9 

•$ 

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283.1 

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241.1 

5476. 

262.3 

± 

6397-I 

283.5 

4 

4641-5 

241-5^ 

,1 

5492-4 

262.7 

•8 

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283.9 

77- 

4656-6 

241.9 

•  4 

5508.8 

263.1 

•2 

6432.6 

284.3 

.* 

4671-7 

242.2 

•4 

5525-3 

263-5 

•8 

6450.4 

284-7 

JL 
*  4 

4686.9 

242.7 

84. 

5541-8 

263.9 

•f 

6468.2 

285-1 

.1 

4702.  i 

243. 

-$ 

5558.3 

264.3 

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6486. 

285.5 

4717-3 

243-5 

JL 
•4 

5574-8 

264.7 

91. 

6503-9 

285-9 

•1 

4732.5 

243.8 

•1 

5591-3? 

265." 

1 

•  H 

6521.7 

286.3 

•f 

4747-8 

244-3 

•I 

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265.5 

6539-7 

286.7 

•8 

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244-6 

.1 

5624-5 

265.8 

•f 

6557-6 

287.1 

78- 

47/8-4 

245- 

•4 

5641.2 

266.2 

•2 

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245-4 

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266.6 

•8 

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287.8 

.1 

4809. 

245-8 

85- 

5674.5 

267.. 

•4 

6611.5 

288.2 

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4824.4 

246.2 

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5691.2 

267.4 

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6629.5 

288.6 

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4839.8 

246.6 

i, 

*4 

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267.8 

92. 

6647.6 

289. 

•i 

4855.2 

247- 

5724-6. 

268.2 

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289.4 

•f 

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5741-5 

268.6 

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6683.8 

289.8 

•8 

4886,1 

247-7 

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268.9 

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6701.9 

290.2 

79- 

4901.7 

24.8.2 

£ 

5775-1 

269.4 

6720.  i 

290.6 

4917.2 

248.5 

•8 

5791-9 

269.7 

•8 

6738.2 

291. 

.; 

4932.7 

249. 

86. 

.5808.8 

270.2 

•4 

6756.4 

291.4 

,j 

4948.3 

249-3 

•^ 

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270.5 

•8" 

6774.7 

291.8 

.; 

4963.9 

249-8 

•? 

5842.6 

271. 

93- 

6792.9 

292.2 

,.j 

4979-5 

250.1 

•8 

5.859-5 

271.3 

3 

6811.1 

292.6 

4995-2 

250.5 

•i 

5876.5 

271.7 

•¥ 

6829.5 

293- 

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5010.8 

250.9 

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5893-5 

272.1 

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6847.8 

293-4 

80.    ' 

5026.5 

251-3 

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591.0.6 

272.5 

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6866.  i 

293-7 

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5042.2 

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5927-6 

272.9 

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6884.5 

294.1 

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252.1 

87. 

5944-7 

273-3 

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6902.9 

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5073.7 

252.5 

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5961-7 

273-7 

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6921.3 

294.9 

5089.6 

252.9 

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5978.9 

274.1 

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6939.8 

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5105.4 

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274.4 

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295-7 

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5121.2 

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6013.2 

274-9 

.; 

6976.7 

296.1 

5I37.I 

254-1 

6030.4 

275.2 

6995-2 

296.5 

81! 

5I53-. 

254-5 

.; 

6047.6 

275-7 

.-.  • 

7013.8 

296:9 

5168.9 

254-9 

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6064.8 

276. 

7032-3 

297-3 

5184.9 

255-3 

88. 

6082.1 

276.5 

7051- 

297-7 

!      5200.8 

255-6 

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6099.4 

276.S. 

•', 

7069.5 

298.1 

.. 

5216.8 

256. 

.; 

6116.7 

277.2 

95- 

7088.2 

298.5 

5232.8 

256.4 

•f 

6134. 

277.6 

7106.9 

298.8 

5248.9 

256.8 

t1  . 

6151.4 

278. 

•4" 

7125-6 

299.2 

,. 

5264.9 

257.2 

6168.8 

278.4 

•8 

7144.3 

299.6 

82. 

528l. 

257.6 

•i  • 

6186.2 

278.8 

J 

7163- 

300. 

294 


Steam  Engine  Indicator 
TABLE  No.  7.— CONTINUED. 


Arecs  and  Circumferences  of  Ci-cles  from   1-64  104  inches  in  diameter,  varying  by  sixteenths; 
aud  f roiu  4  inches  to  100  inches,  varying  by  one-eighth  inch. 


Diam. 
in 
Iiiches. 

Area 
in  Square 
Inches. 

Circum. 
in 
Inches. 

Diam. 
in 
Inches. 

Area 
in  Square 
Inches. 

Circum. 
in 
Inches. 

Diam. 
in 
Inches. 

Area 
in  Square 
Inches. 

Circum. 
in 
Inches. 

95-  1 

7181.8 

300:4 

97-  1 

7408.8 

305.1 

98  | 

7639-4 

309.8 

•4 

720O.6 

300.8 

7428. 

305-5 

76589 

310.2 

-! 

7219.4 

301.2 

| 

7447- 

305-9 

| 

7678.2 

310.6 

96 

7238.2 

301.6 

I 

7466.2 

306.3 

99 

769'  7 

311. 

4 

7257.1 

302. 

§ 

7485.3 

306.7 

7717.1 

3H-4 

-? 

7276. 

302.4 

2 

7504-5 

307.1 

•i 

7736.6 

311.8 

.g 

7294.9 

302.8 

2 

7523-7 

307-5 

1 

7756-I 

312.2 

JL 

7313-8 

303.2 

98 

7543- 

307.9 

j 

7775-6 

312.6 

if 

7332-8 

303-5 

7562.2 

308.3 

| 

7795-2 

3!3- 

•f 

7351.8 

303.9 

± 

7581.5 

308.7 

| 

7814.8 

3^34 

'# 

7370.7. 

304.3 

f 

7600.8 

309. 

i 

7834.3 

313.8 

97- 

•7389.8 

304.7 

I 

7620.  i 

309-4 

100. 

7854. 

314  2 

If  the  areas  of  larger  circles  are  required,  they  w'll  be  found 
by  the  following : 

RULE — Multiply  the  square  of  the  diameter  in  inches,  by 
the  decimal  0.7854,  and  the  product  will  be  the  area  in  square 
inches ;  or,  multiply  half  the  circumference  by  half  the  diam- 
eter. If  the  circumference  of  a  larger  circle  is  wanted,  and 
having  the  diameter,  the  rule  is  as  follows : 

RULE — As  7  is  to  22,  so  is  the  diameter  to  the  circumfer- 
ence, or  diameter  multiplied  by  3.1416  equal  circumference. 


And  Its  Appliances. 


295 


TABLE  No.  8. 

The  properties  of  Saturated  Steam. 


PRESSUEB  PER 
SQUARE  INCH. 

Temp- 
erature in 
Fahrenheit 
Degrees. 

NUMBER  ofr  BRITISH  THERMAL  UNITS  IN 
ONE  POUND  FROM  ZEBO  (FAHRENHEIT). 

Weight 
of  One 

Cubic 
Foo^  of 
Steam 
in 
Decimals 
of  a 
Pound. 

dumber 
of 
Cubic 
Feet  of 
Steam 
from  One 
Cubic 
Foot  of. 
Water. 

Total 
Pressure 
iu 
Pounds 
Jroui  u 
Vacuum 

Pressure 
in  Pounds 
as 
Shown  by 
Steam 
Gauge. 

Number 
of  Units  of 
Heat  in 
Water. 

Number  of 
Units  of  Heat 
Required  for 
Evaporation, 
Called 
Latent  Heat. 

Total 
Number 
of  Units  of 
Heat 
Contained 
in  Steam. 

\ 

102. 

102.086 

1042.964 

1145.050 

.0030 

20620.0 

•2 

126.263 

126.440 

1026.010 

1152.450 

.0058 

10720.0 

3 

141.622 

141.877 

1015.254 

1157.131 

.0085 

7326.0 

4 

153.070 

153.396 

1007.229 

1160.625 

.0112 

5600.0 

5 

162.330 

162.722 

1000.727 

1163.449 

.0137 

4535.0 

G 

170.123 

I7o!577 

995^249 

1165.826 

.0163 

3814.0 

7 

176.910 

177.425 

990.471 

1167.896 

.0189 

3300.0 

"8 

182.910 

183.481 

986.245 

1169.726 

;0214 

2910.0 

9 

188.316 

188.941 

982.434 

1171.375 

.0239 

2607.0- 

id 

193.240 

193.919 

978.958 

1172.877 

.0264 

2360.0 

11 

19t.768 

198.496 

975.762 

1174.258 

.0289 

2157.0 

12 

201.960 

202.737 

972.800 

1175.537 

.•'313 

1988.0 

13 



205.8S5 

206.709 

970.025 

1176.734 

.0337 

1846.0 

14 

209.560 

210.428 

967.427 

1177.855 

.0362 

1722.0 

14  7 

212.000 

212.900 

965.700 

1178.600 

03797 

1644.0 

15 

.304 

213.025 

213.939 

964^973 

117&912 

.0:187 

1612.0 

16 

1.304 

216.296 

217.252 

962.657 

1179.909 

.0413 

1514.0 

17 

2.304 

219.410 

220.409 

960.450 

1180.859 

.0437 

1427.0 

18 

3.304 

222.378 

223.419 

958.345 

1181.764 

.0462 

1350.6 

19 

4.304 

225.203 

226.285 

956.343 

1182.628 

.0487 

1282.1 

20 

5.304 

227.917 

229.039 

954.415 

1183;454 

.0511 

1220.3 

21 

6.304 

230.515 

231.676 

.952.570 

1184.246 

.0536 

1164.4 

22 

7.304 

233.017 

234.218 

950.791 

1185.009 

.0561 

1113.5 

23 

8.304 

235.432 

236.672 

949.072 

1185.744 

.0585 

1066.9 

24 

9.304 

237.752 

239.029 

947.424 

1186.453 

.0610 

1024.1 

25 

10.304 

240.000 

241.314 

945.825 

1187.139 

.0634 

984.8.' 

26 

11.304 

242.175 

243.526 

944.277 

1187.803 

.0658 

948.4 

27 

12.304 

244.284 

245.671 

942.775 

1188.446 

.0683 

914,6- 

28 

13.304 

246.326 

247.748 

941.321 

1189.069 

.0707 

883.2 

29 

14.304 

248.310 

249.769 

939.905 

1189.674 

.0731 

854'.0 

30 

15.304 

250.245 

251.738 

938.925 

1190.263 

.0755 

826*8 

31 

16.304 

252.122 

253.648 

937.1878 

1190.8358 

.0779 

801.2 

32 

17.304 

253.952 

255.512 

935.8818 

1191.3938 

.0803 

777.2; 

33 

18.304 

255.735 

257.329 

934.60S8 

1191.9378 

.0827 

754.7 

34 

19.304 

257.476 

259.103 

933.3658 

1102.4688 

.0851 

733.5 

35 

20.304 

259.176 

260.835 

932.1523 

1192.9873 

.0875 

713.4 

36 

21.304 

260.835 

262.527 

930.9668 

1193.4938 

.0>99 

694.5 

37 

22.304 

262.458 

264.182 

929.8068 

1193.9888 

.0922 

676.6 

38 

23.304 

264.045 

265.801 

928.6718 

1194.4728 

.0946 

659.7 

39 

24.304 

265.599 

267.386 

927.5608 

1194.9468 

.0970 

643.6 

40 

25.304 

267.120 

268.938 

926.4728 

1195.4108 

.0994 

628.2 

41 

26.304 

268.611 

270.460 

925.4058 

1195.8658 

.1017 

613.4 

42 

27.304 

270.073 

27-1.954 

924.3578 

1196.3118 

,1041 

599.3 

43 

28.304 

271.507 

273.417 

923.33J3 

1196.7493 

.1064 

586.1 

44 

29.304 

272.915 

574.855 

922.3238 

1197.1788 

.1088 

573.7 

45 

30.304 

274.296 

276.266 

921.3343 

1197.6003 

.1111 

561.8 

46 

31.304 

275.652 

277.651 

920.3632 

1198.0142 

.1134 

550.4 

47 

32.304 

276.986 

,279.016 

919.4052 

1198.4212 

.1158 

539.5 

48 

33.304 

278.297 

280.355 

918:4602 

1198.8212 

.1181 

529.0 

49 

34.304 

279.585 

281.672 

917.5422 

1199.2142 

.1204 

518.6 

50 

35.304 

280.854 

282.969 

916.03  16 

1199.6006 

.1227 

508.5 

51 

36.304 

282.099 

284.243 

915.7377 

1199.9807- 

.1251 

499.1 

52 

37.304 

283.326 

285.499 

914.8557 

1200.3547 

.1274 

490.1 

296 


Steam  Engine  Indicator 


TABLE  No.  8. — CONTINUED. 

The  Properties  of  Saturated  Steam. 


PRESSURE  PEB 
SQUARE  INCH. 

Temp- 
erature in 
Fahrenheit 
Degrees. 

NUMBER  OF  BRITISH  THERMAL  UNITS  IN 
ONE  POUND  FROM  ZERO  (FAHRENHEIT). 

Weight 
of  One 
Cubic 
Foot  of 
Steam 
in 
Deci  mals 
of  a 
Pound. 

Number 
of 
Cubic 
Feet  of 
Steam 
from  One 
Cubic 
Foot  of 
Water. 

Total 
Pressure 
in 
Pounds 
from  a 
Vacuum 

Pressure 
in  Pounds 
as 
Shown  hy 
Steam 
Gauge. 

Number 
of  Units  of 
Heat  in 
Water. 

Number  of 
Units  of  Heat 
Required  for 
Evaporation, 
Called 
Latent  Heat. 

Total 
Number 
of  Units  of 
Heat 
Contained 
in  Steam. 

53 

38.304 

284.534 

286.736 

913.9871 

1200.7231 

.1297 

481.4 

•54 

39.304 

285.724 

287.952 

913.1340 

1201.0860 

.1320 

472.9 

55 

40.304 

286.897 

289.153 

912.2906 

1201.4436 

.1343 

464.7 

56 

41.304 

288.052 

290.335 

911.4611 

1201.7961 

.1366 

457.0 

57 

42.304 

289.112 

291.503 

910.6407 

1202.1437. 

.1388 

449.6 

58 

43.304 

290.316 

292.654 

909.8325 

1202.4865 

.1411 

442.4 

59 

44.304 

291.425 

293.790 

909.0346 

1202.8246 

.1434 

435.3 

60 

45.304 

292.520 

294.911 

908.247.2 

1203.1582 

,1457. 

428.5 

61 

46.304 

293.598 

296.016 

907.4713 

1203.4873 

.14793 

422.0 

62 

47.304 

294.663 

297.108 

906.7042 

1203.8122 

.15021 

415.6 

63 

48.304 

295.714 

298.185 

9U5.9477 

1204.1329 

.15248 

409.4 

64 

49.304 

296.752 

299.249 

905.2005 

1204.4495 

.15471 

403.5 

65 

50.304 

297.7J7 

300.300 

904.4621 

1204.7621 

.15697 

397.7 

66 

51.304 

298.789 

301.338 

903.7327 

1205.07U7 

.15921 

3921 

67 

52.304 

299.789 

302.364 

903.0116 

1205.3756 

.16147 

386.0 

68 

53.304 

300.776 

303.377 

902.2999 

1205.6769 

.16372 

381.3 

69 

54.304 

301.753 

304.380 

901.5947 

1205.9747 

.16598 

376.1 

70 

55.304 

302.718 

305.370 

900.8991 

1206.2691 

.16817 

371.2 

71 

56.304 

303.673 

306.350 

900.2101 

1206.5601 

.170o8 

366.4 

72 

'57.304 

304.617 

307.320 

899.5280 

1  200.8480 

.1725'.) 

361.7 

73 

58.304 

305.551 

308.279 

898.8537 

1207.1327 

.17481 

357.1 

74 

59.304 

306.474 

309.228 

898.1863 

1207.4143 

.17704 

3.32.6 

75 

60.304 

307.388 

310.166 

897.52*9 

1207.6929 

.179-'3 

348.3 

76 

61.304 

308.290 

311.092 

898.8764 

1207.9684 

.18142 

344.1 

77 

62.304 

309.184 

312.0U 

896.2301 

1208.2411 

.18360 

340.0 

78 

63.304 

310.069 

312.920 

895.5910 

1208.5110 

.18579 

336.0 

79 

64.304 

310.945- 

313.821 

894.9571 

r.'OS.778L 

.18797 

332.1 

80 

65.304 

311.812 

314.712 

894.3304 

1209.0424 

.19015 

328.3 

81 

66.304 

312.670 

315.595 

893.7092 

1  209.3042 

.19232 

324.6 

82 

67.304 

313.520 

316.468 

893.0954 

1209.5634 

.19454 

320.9 

83 

68.304 

314.361 

317.333 

892.4871 

1209.8201 

.19674 

317.3 

84 

69.304 

315.195 

318.190 

891.8843 

1210,0743 

.19887 

313.9 

85 

70.304 

316.021 

319.040 

891.2862 

.1210.3262 

.20105 

310.5 

86 

71.304 

316.839 

319.882 

890.6938 

1210.5758 

.20321 

307.2 

87 

72304 

317.650 

320.717 

890.1061 

1210.8231 

.2053-3 

304.0 

88 

73.304 

318.453 

321.543 

889.5251 

1211.0681 

.20753 

300.8 

89 

74.3U4 

319.249 

322.362 

888.9490 

1211.3110 

.20970 

297.7 

90 

73.304 

320.039 

323.176 

888.3758 

1211.5518 

.21183 

204.7 

91 

76.304 

320.821 

323.981 

887.8094 

1211.7904 

.21303 

291.3 

92 

77.304 

321.597 

324.781 

887.2460 

1212.0270 

.21608 

288.9 

03 

78.304 

322.266 

325.572 

886.6896 

1212.2616 

.21820 

28(5.1- 

94 

79.304 

323.128 

326.358 

886.1362 

1212.4942 

.22043 

283.3 

95 

80.304 

323.884 

327.136 

885.5887 

1212.-7247 

.22247 

280.6 

96 

81.304 

324.634 

327.909 

885.0444 

1212.9534 

.22455 

278.0 

97 

82.304 

325.378 

328.675 

884.5052 

1213.1802 

.22667 

275.4 

98 

83.304 

326.114 

329.433 

'883,972r 

1213.4051 

.22883 

272.8 

99 

84.304 

326.845 

330.186 

883.4421 

1213.6281 

.23095 

270.3 

100 

85.304 

327.571 

330.935 

882.9144 

1213.8494 

.23302 

267.9 

101 

86.304 

328.291 

331.678 

882.3909 

12  14.0689 

.23510 

265.5 

102 

87.304 

329.005 

332.414 

881.8727 

1214.2867 

.23717 

263.2 

103 

88.304 

329,714 

333.145 

881.3577 

1214.5027 

.23925 

260.9 

104 

89.304 

330,416 

333.869 

880.8481 

1214.7171 

.24132 

258.7 

105 

90.304 

331.113 

V334.587 

880.3429 

1214.9299 

.24340       256.5 

And  Its  Appliances. 


297 


TABLE  No.  8.— CONTINUED. 

The  Properties  of  Saturated  Steam. 


PRESSURE  PER 
SQUARE  INCH. 

Temp- 
erature in 
Fahrenheit 
Degrees. 

NUMBER  OF  BRITISH  THERMAL  UNITS  IN 
ONE  POUND  FROM  ZERO  (FAHRENHEIT). 

Weight 
of  On« 
Cubic 
Foot  of 
Steam 
in 
Decimals 
of  a 
Pound. 

Number 
of.    * 
Cubic 
Feet  of 
Steam 
rom  One 
Cubic 
Foot  of 
Water. 

Total 
Pressure 
in 
Pounds 
from  a 
Vacuum 

Pressure 
in  Pounds 
as 
Shown  by 
Steam 
Gauge. 

Number 
of  Units  of 
Heat  in' 
Water. 

Number  of 
Fiiitsof  Heat 
Required  for 
Evaporation, 
Called 
Latent  Heat. 

Total 
Number 
of  Units  of 
Heat 
Contained 
in  Steam. 

106 

91.304 

331.805 

335.301 

879.8400 

1215.1410 

.24547 

254.3 

107 

92.304 

332.492 

336.009 

879.3416 

•1215.3506 

.24754 

252.2 

108 

93.304 

333.174 

336.714 

878.8447 

1215.5587 

.24961 

250.1 

109 

94.304 

333.851 

337.411 

878.3542 

1215.7652 

.25168 

248.0 

110 

95.304 

334.523 

338.105 

877.8653 

1215.9703 

.25376 

246.0 

111 

96.304 

335.191 

338.795 

877.3789 

1216.1739 

.25582 

244.0 

112 

97.304 

335.854 

339.479 

876.8970 

1216.3760 

.25788 

242.0 

113 

98.304 

336.511 

340.157 

876.4198 

1216.5768 

.25994 

240.1 

114 

99.304 

337  165 

340.832 

875.9442 

1216.7762 

.26199 

238.2 

115 

100.304 

337.814 

341.502 

875.4721 

1216.9741 

.26405 

236.3 

116 

101.304 

338.459 

342.169 

875.0018 

1217.1708 

.26611 

234.5 

117 

102.304 

339.100 

342.831 

874.5352 

1217.3662 

.26816 

232.7 

118 

103.304 

339.736 

343/488 

874.0722 

1217.5602 

.27020 

231.0 

119 

104.304 

340.3US 

o44.141 

.873.5120 

1217.7530 

.27224 

229.3 

120 

105.304 

34U.995 

o44.789 

873.1555 

1217.9445 

.27428 

227.6 

121 

106.304 

341.618 

345.432 

872.7027 

1218.1347 

.27(528 

226.0 

122 

107.304 

342.238 

346.073 

872.25D8 

1218.3238 

.27828 

224.4 

123 

108.304 

342.854 

346.709 

871.8027 

1218.5117 

.28027 

222.8 

124 

109.304 

343.466 

347.343 

871.3553 

1218.6983 

.28227 

221.2 

125 

110.304 

344.074 

347.972 

870.9118 

1218.b838 

.28426 

219.7 

126 

111.304 

344.678 

348.596 

870.4721 

1219.0681 

.28625 

218.2 

127 

112.304 

345.279 

349.217 

870.0342 

1219,2512 

.28824 

216.7 

128 

113.304 

345.876 

349.833 

869.5983 

1219.4333 

.29023 

215.2 

129 

114.304 

346.459 

350.448 

869.1663 

1219.6143 

.29222 

213.7 

130 

115.304 

347.059 

351.059 

868.7351 

1219.7941 

.29420 

212.3 

131 

1.16.304 

347.644 

351.665 

868-3079' 

1219.9729 

.29618 

210.9 

132 

117.304 

348.22:7 

352.267 

867.8836 

1220.1506 

.29816 

209.5 

133 

118.304 

348.806 

352.867 

867.4601 

1220.3271 

.30013 

208.1 

134 

119.304 

349.382 

353.463 

867.0397 

1220.5027 

.30209 

206.7 

135 

120.304 

349.954 

354.055 

866.6223 

1220.6773 

.30405 

205.4 

136 

121.304 

350.523 

354.644 

866.2068 

1220.8508 

.30601 

204.1 

137 

122.304 

351.089 

355.230 

866.7934 

1221.0234 

.30796 

202.8 

138 

123.304 

351.752 

355.813 

865.3820 

1221.1950 

.30990 

201.5 

139 

124.304 

352.211 

356.392 

864.9735 

1221.3655 

.31186 

200.2 

140 

125.304 

352.767 

356.969 

864.5661 

1221.5351 

.31386 

199.0 

141 

126.304 

353.319 

357.541 

864.1627 

1221.7037 

.31587 

197.8 

142 

127.304 

353.869 

358.110 

863.7613 

1221.8713 

.31788 

196.6 

143 

128.304 

354.416 

358.677 

863.3611 

1222.0381 

.31990 

195.4 

144 

129.304 

354.960 

359.240 

862.9640 

1222.2040 

.32190 

194.2 

145 

130.304 

355.501 

359.801 

862.5679 

122  .'.3689 

.32391 

193.0 

146 

131.304 

356.039 

360.359 

862.1740 

1222.5330 

.32592 

191.9 

147 

132.304 

356.574 

360.913 

861.7832 

1222.6962 

.32794 

190.8 

148 

133.304 

357.106 

361.465 

861.3934 

1222.8584 

.32995 

189.7 

149 

134.304 

357.635 

362.013 

861.<»068 

1223.0198 

.33196 

188.6 

150 

135.304 

358.161 

3t>2.559 

860.6213 

1223.1803 

.33400 

187.5 

151 

136.304 

358.683 

363.100 

860.2399 

1223.3399 

.33580 

186.4 

152 

137.304 

359.203 

363.640 

859.8588 

1223.4988 

.33761 

185.3 

153 

138.304 

359.721 

364.177 

859.4799 

1223.6569 

.33942 

184.3 

154 

139.304 

360.236 

364.711 

859.1031 

1223.8141 

.34123 

183.3 

155 

140.304 

360.749 

.  365.243 

858.7276 

1223.9706 

-.34304 

182.3 

156 

141.304 

361.260 

365.773 

858.3533 

1224.1263 

.34485 

181.3 

157 

142.304 

361.768 

366.300 

857.9811 

1224.281  1 

.34666 

1S0.3 

'  158 

143.304 

362.273 

366.824 

857.6112 

1224.4352 

.34847 

1  79.3 

298 


Steam  Engine    Indicator 


TABLE  No.  8.— CONTINUED. 

The  Properties  of  Saturated  Steam. 


PRESSURE  PER 
SQUARE  INCH. 

Temp- 
erature in 
Fahrenheit 
Degrees. 

NUMBER  OF  BRITISH  THERMAL  IJNITS  IN 
ONE  POUND  FROM  ZERO  (FAHRENHEIT). 

Weight 
of  One 
Cubic 
Foot  of 
Steam 
in 
Decimals 
of  a 
Pound. 

Number 
of 
Cubic 
Feet  of 
Steam 
roru  One 
Cubic 
Foot  of 
Water. 

Total 
Pressure 
in 
Pounds 
from  a 
Vacuum 

Pressure 
in  Pounds 
as 
Shown  by 
Steam 
Gauge. 

Number 
of  Units  of 
Heat  in 
\Vater. 

Number  of 
Units  of  Heat 
Required  lor 
Evaporation, 
Called 
Latent  Heat. 

Total 
Number 
of  Units  of 
Heat 
Contained 
in  Steam. 

159 

144.304 

362.776 

367.347 

857.2415 

1224.5885 

.35028 

178.3 

160 

145.304 

363.277 

367.867 

856.8740 

1224.7410 

.35209 

177.3 

161 

146.304 

363.774 

368.383 

856.5099 

1224.8929 

.35397- 

176.4 

162 

147.304 

364.270 

368.898 

856.1461 

1225.0441 

.35585 

175.5 

163 

L48.3U4 

364.764 

369.410 

855.7846 

122511946 

.35773 

174.6 

164 

149.304 

365.255 

369.920 

855.4243 

1225.3443 

.35961 

173.7 

165 

150.304 

365.744 

370.428 

855.0654 

1225.4934 

.36149 

172.8 

166 

151.304 

366.232 

370.934 

854.7077 

1225.6417 

.36337 

171.9 

167 

152.304 

366.717 

371.438 

854.3514 

1225.7894 

.36525 

171.0 

168 

153.304 

367.199 

371.939 

853.9974 

1225.9364 

.36714 

170.1 

169 

154.304 

367.680 

372.437 

853.6456 

1226.0826 

.36903 

169.2 

170 

155.304 

368.158 

372.934 

853.2942 

1226.2282 

.070!  12 

168.4 

171 

156  304 

368.632 

373.427 

852.9461 

1226.3731 

.37272 

167.6 

172 

157.304 

369.105 

373.918 

852.5995 

1226.5175 

.37452 

166.8 

17.5 

158.304 

369.576 

374.408 

852.2533 

1226.6613 

.37632 

166.0 

174 

159.3d4 

370.045 

374.895 

851.9094 

1226.8044 

.37812 

165.2 

17> 

160.304 

370.512 

375.380 

851.5670 

1226.9470 

.37992 

164.4 

176 

161.304 

370.978 

375.865 

851.2239 

1227.0889 

.38172 

163.6 

177 

162.304 

371.442 

376.347 

850.8833 

1227.2303 

.38353 

162.8 

178 

163.304 

371.904 

376.827 

850.5441 

1227.3711 

.38534 

162.0 

179 

164.304 

372.364 

377.305 

850.2062 

1227.5112 

.38715 

161.2 

180 

165.304 

372.822 

377.781 

849.8698 

1227.6508 

.38895 

160.4 

181 

166.304 

373.275 

378.255 

849.5347 

1227.7897 

.39077 

159.7 

182 

167.304 

373.731 

378.727 

849.201  1 

1227.9281 

.39259 

159.0 

183 

168.304 

374.183 

379.197 

848.8689 

1228.0659 

.39441 

158.3 

184 

169  304 

374.633 

279.665 

848.5380 

1228.2030 

.39624 

157.6 

185 

170.304 

375.081 

380.131 

848.2086 

1  228.3396 

.39807 

156.9 

186 

171.304 

375.527 

380.595 

847.8805 

1228.4755 

.39990 

156.2 

187 

172304 

375.971 

381.056 

847.5549 

1228.6109 

.40173 

155.5 

188 

173.304 

376.413 

381.516 

847.2297 

1228.7457 

.40356 

154.8 

189 

174.304 

376.853 

381.974 

846.9058 

1228.8798 

.40539 

154.1 

190 

175.304 

377.291 

382.429 

846.5844 

1229.0134 

.40722 

153.4 

191 

176.304 

377.727 

382.883 

846.2633 

1229.1463 

.40899 

152.7 

192 

177.304 

378.161 

383.335 

845.9437  « 

1229.2787 

.41076 

152.0 

193 

178.304 

378.593 

383.785 

845.6256 

1229.4106 

.41253 

151.3 

194 

179.304 

379.023 

384.233 

845.3089 

1229.5419 

.41430 

150.7 

195 

180.304 

379.452 

384.679 

844.9938 

1229.6728 

.41607 

150.1 

196 

181.304 

379.979 

385.123 

844.6801 

1229.8031 

.41784 

149.5 

197 

182.304 

380.305 

385.567 

844.3660 

1229.9330 

.41962 

148.9' 

198 

183.304 

380.729 

386.008 

844.0543 

1230.0623 

.42140 

148.3 

199 

184.304 

381.152 

386.449 

843.7422 

1230.1912 

.42318 

147.7 

200 

185.304 

381.573 

386.887. 

843.4326 

12303196 

.42496 

147.1 

2Q1 

1  86.304 

381.992 

387.324 

843.1234 

1230.4474 

.42667 

146.5 

202 

187.304 

382.410 

387.760 

842.8148 

1230.5748 

.42838 

145.9 

203 

188.304 

382.827 

388.194 

842.5076 

1230.7016 

.43009 

145.3 

204 

189.304 

383.242 

388.627 

842.2010 

1230.8280 

.43180 

144.7 

20:> 

190.304 

383.655 

389.057 

841.8969 

1230.9539 

.43351 

144.1 

206 

191.304 

384066 

389.485 

841.5942 

1231.0792 

.43523 

143.5 

207 

192.304 

384.475 

389.912 

841.2921 

1231.2041 

.43695 

142.9 

208 

193.304 

384.883 

390.337 

840.9914 

1231.3284 

.43866 

142.3 

209 

194.304 

385.2K8 

390.759 

840.6933 

1231.4523 

.44039 

141.8 

210 

195.304 

385.671 

391.179 

840.3967 

1231.5757 

.44211 

141.3 

And  its  Appliances. 


2  99 


TABLE  No.  9. 

The  Properties  cf  Water  from  32°  to  212°  Fahrenheit. 


KI.ASTIC  FORCE. 

Tem- 
perature 
in  Fah- 
renheit 
Degrees. 

NUMBER  OF  BRITISH  THERMAL  UNITS  IN 
ONE  POUND  FROM  ZERO  (FAHRENHEIT). 

Weight 
of  One 
Cubic 
Foot  of 
Vapor 
in 
Decimals 
of  a  • 
Pound. 

Number 
of 
Cubic 
Feet  of 
Steam 
from  One 
Cubic 
Foot  of 
\Vater. 

In  Pounds 
on  thk 

Square 
Inch. 

In  Inches 
cf 
Mercury. 

Number 
of  Units  of 
Heat  in 
Water 

Number  of 
Units  of  Heat 
Required  for 
Evaporation, 
Called 
Latent  Heat. 

Total 
Number 
of  Units  of 
Heat 
Contained 
in  Vapor. 

.080 

.1311 

32 

32.000 

1091.700 

1123.700 

.00030 

208,080 

.092 

.1884 

33 

33.000 

1091.005 

1124.005 

.00030 

200,480 

.Oi!S 

.1960 

34 

34.000 

.1090.310 

1124.310 

.00031 

193,180 

.100 

.2039 

35 

35.000 

1089.615 

1124.615 

:00032 

186,180 

.104 

.2121 

36 

36.000 

1088.920 

1124.920 

.00033 

179,380 

.103 

.2205 

37 

37.000 

1088.225 

1125.225 

.00034 

172,780 

.112 

.2292 

38 

38.000 

1087.530 

1125.530 

.00036 

166,380 

.117 

.2382 

39 

39.001 

1086.834 

1125.835 

.C0038 

160,230 

.122 

.2476 

40 

40.001 

1086.139 

1126.140 

.00040 

T54.330 

.127 

.2573 

41 

41.001 

1085.444 

1123.445 

.00042 

148,620 

.132 

.2673 

42 

42.001 

1084.749 

1126.750 

.00913 

143,220 

.137 

.2777 

43 

43.001 

1084.054 

1127.055 

.00045 

138,070 

.142 

.2884 

44 

44.002 

1083.358 

1127.360 

.00047 

133,120 

.1-17 

,2994 

45 

45.002 

1082.663 

1127.665 

.00049 

128,370 

.152 

.3109 

46 

46.002 

1031.968 

1127.970 

.00050 

123,840 

"    .138 

.3228 

47 

47.002 

1081.273 

1128.275 

.CC052 

119,610 

.104 

.3351 

48 

48.003 

1080.577 

1128.580 

.C0054 

115,490 

.170 

.3478 

49 

49.003 

1079.882 

1128.885 

.CG05G 

111,470 

.176 

.3608 

50 

50.003 

1079.187 

1129.190 

.00053 

107,630 

-.183 

.3743 

51 

51.004 

1078.491 

1  129.495 

.COC30 

103,930 

.190 

.3883 

52 

52.004 

1077.796 

1129.800 

.COOC2 

100,330 

.197 

.4028 

53 

53.005 

1077.100 

1130.105 

.00065 

96,930 

.205 

.4177 

54 

54.005 

1076.405 

1130.410 

.00067 

93,680 

.212 

.4332 

55 

55.006 

1075.709 

1130.715 

.00069 

90,540 

.220 

.4492 

56 

56.006 

1075.014 

1131.020 

.C0071 

87,500 

.228 

.4656 

57 

57.007 

1074.318 

1131.325 

.00073 

84,560 

.236 

.4825 

58 

58.007 

1073.623 

1131.630 

.00076 

81,740 

.245 

.5000 

59 

59.008 

1072.927 

1131.935 

.00079' 

79,020 

.254 

.5180 

60 

60.009 

1072.231 

1  132.240 

.00082 

76,370 

.263 

.5367 

61 

61.010 

1071.535 

1132.545 

.00085 

73,810 

.273 

.5560 

62 

62.011 

1070.839 

1132.850 

.00088 

71,330 

0^2 

.5758 

63 

63.012 

1070.143 

1133.155 

.OOC91 

68,940 

o<)2 

.5962 

64 

6-1.013 

1069.447 

1133.460 

.00094 

66,630 

[302 

.6173 

65 

65.014 

1068.751 

1133.765 

.00097 

64,420 

.313 

.6391 

66 

66.015 

1068.055 

]  134.070 

.00100 

62,290 

.324 

.6615 

67 

67.016 

1067.359 

1134.375 

.00103 

00,280 

.335 

.G846 

68 

68.01S 

1066.662 

1134.680 

.00107 

58,340 

.347 

.7084 

69 

69.019 

1065.966 

1134.985 

.00111 

56,470 

.359 

.7330 

70 

70.020 

1065.270 

1135.290 

.00115 

54,660 

.372 

.7583 

71 

71.021 

1064.574 

1135.595 

-.00119 

52,910 

:.385 

.7844 

72 

72.023 

1063.877 

1135.900 

.00123 

51,210 

'.398 

.8114 

73 

73.024 

1063.181 

1136.205 

.00127 

49,570 

.-111 

.8391 

74 

74.026 

1062.484 

1136.510 

.00131 

48,000 

.425 

.8676 

75 

75.027 

1061.788 

1136-815 

.00135 

46,510 

.440 

.8969 

76 

76.029 

1061.091 

1137.120 

.00139 

45,060 

.455 

.9271 

77 

77.030 

1060.395 

1137.425 

.00143 

43,650 

.470 

.9583 

78 

78.032 

1059.698 

1137.730 

.00148 

42,280 

.486 

.9905 

79 

79.034 

1059.001 

1138.035 

.00153 

40,960 

.502 

1  .023 

80 

80.036 

1058.304 

1138.340 

.00158 

39,690 

.518 

1.056 

81 

81.037 

1057.608 

1138.645 

.00163 

.  38,480 

.535 

1.091 

82 

82.U39 

1056.91  1 

1138.950 

.00168 

37,320 

300 


Steam  Engine  Indicator 


TABLE  No.  9.— CONTINUED. 

The  Properties  of  Water  from  32°  to  212°  Fahrenheit. 


ELASTIC  FORCE. 

Tem- 
perature 
in  Fah- 
renheit 
Degrees. 

NUMBER  OF  BRITISH  THERMAL  UNITS  IN 
ONE  POUND  FROM  ZERO  (FAHRENHEIT). 

Weight 
of  One 
Cubic 
Foot  of 
Vapor 
in 
Decimals 
of  a 
Pound, 

Number 
of 
Cubic 
Feet  of 
Steam 
rom  0,n  e 
cubic 
Footo! 
\N  ater. 

In  Pounds 
on  the 
Square 
Inch. 

In  Inches 
of 
Mercury. 

Number 
of  Units  of 
Heat  in 
Water. 

Number  of 
Units  of  Heat 
Required  for 
Evaporation, 
Called 
Latent  Heat. 

Total 
Number      j 
of  Units  of 
Heat 
Contained 
in  Vapor. 

.553 

1.127 

83 

83.041 

1056.214 

1139.255 

.00173 

36.1UO 

.571 

1.163 

84 

84.043 

1055.517 

1139.560 

.00178 

£5,100 

.590 

1.201 

85 

.  85.045 

1054.820 

11C9.S65 

.00183 

34,050 

.609 

1:240 

86 

86.047 

1054.123 

1140.170 

.00189 

33,030 

.629 

1.281 

87 

87.049 

1053.426 

1140.475 

.00195 

32,050 

,650 

1.323 

88 

88.051 

1052.729 

1140.780 

-.00201 

31,100 

.671 

1.366 

89 

89.053 

1052.C32 

1141.085 

.00207 

30,180 

.692 

1.410 

90 

90.055 

1051.335 

1141.390 

.00213 

29,290 

.715 

1.454 

91 

91.057 

1050.638 

1141.695 

.00219 

28,430 

.738 

1.500 

92 

92.059 

1049.941 

1142.000 

.00226 

27,600 

.761 

1.548 

93 

93.061 

1049.244 

1142.305 

.00233 

26,800 

.785 

1.597 

94 

94.063 

1048.547 

1142.610    i 

.00240 

26020 

.809 

1.647 

95 

95.065 

1047.850 

1142.915 

.00247 

25,270 

.834 

1.698 

96 

96.0G8 

1047.152 

1143.220 

.00254 

24,540 

.860 

1.751 

97 

97.071 

1046.454 

1143.525 

.00262 

23,830 

.887 

1.805 

98 

98.074 

1045.756 

1143.830 

.00270 

23,140 

.914 

1.861 

99 

99.077 

1045.058 

1144.135 

.C0278 

22,470 

.943 

1.918 

100 

100.080 

1044.360 

1144.440 

.00286 

21,830 

.972 

1.977 

101 

101.083 

1043.662 

1144.745 

.00294 

21,210 

1.001 

2.037 

102 

102.086 

1042.964 

1145.050 

.00302 

20,620 

1.031 

2.099 

103 

103.089 

1042.266 

1145.355 

.00311 

20,050 

1.062 

2.163 

104 

104.092 

1041.  f.68 

1145.660 

.00320 

19,500 

1.094 

2.227 

105 

105.095 

1040.870 

1145.965 

.OC330 

18,970 

1.126 

2.293 

1C6 

106.098 

1040.172 

1146.270 

.00340 

18,460 

1.159 

2.361 

107 

107.101 

1039.474 

1143.575 

.00350 

17,960 

1.193 

2.431 

108 

108.104 

1038.776 

1143.880 

.00360 

17,470 

1.229 

2.503 

109  ' 

109.107 

1038.078 

1147.185 

.00370 

16,990 

1.265 

2.577 

110 

110.110 

1037.380 

1147.490 

.00380 

16,520 

1.302 

2.653 

111 

111.113 

1036.682 

1147.795 

.00390 

16,070 

1.341 

2.731 

112 

112.117 

1035.983 

1148.100 

.00400 

15,640 

1.381 

2.810 

113 

113.121 

1035.284 

1148.405 

.00410 

15,220 

1.421 

2.892 

114 

114.125 

1034.585 

1148.710 

.00421 

14,820 

1.462 

2.976 

115 

115.129 

1033.886 

1149.015 

.00433 

14,430 

1.504 

3.061 

116 

116.133 

1033.187 

1149.320 

.00445 

14,050 

1.547 

3.149 

117 

117.137 

1032.488 

1149.625 

.00457 

13,680 

1.591 

3.239 

118 

118.141 

1031.789 

1149.930 

.00470 

13,320 

1.636 

3.331 

119 

119.145 

1031.090 

1150.235 

.00483 

12.970 

1.682 

3.425 

120 

120.149 

1030.391 

1150.540 

.00496 

12^30 

1.730 

3.522 

121 

121.153 

1029.692 

1150.845 

.00508 

12,300 

1.779 

3.621 

122 

122.157 

1028.993 

1151.150 

.00521 

11,980 

1.828 

3.723 

123 

123.161 

1028.294- 

1151.455 

.00535 

11,670 

1.879 

3.826 

124 

124.165 

1027.595 

1151.760 

.00549 

11,370 

1.931 

3.933 

125 

125.169 

1026.896 

1152.065 

.00563 

11,080 

1.984 

4.042 

126 

126.173 

1026.197 

1152.370 

.00578 

10,800 

2.039 

.     4.153 

127 

127.177 

1025.498 

1152.675 

.00593 

10,530 

2.096 

4.267 

128 

128.132 

1024.798 

1152.980 

.00608 

10,265 

2.154 

4.384 

129 

129.187 

1024.098 

1153.285 

.00824 

10,010 

2.213 

4.503 

130 

130.192 

1023.398 

1153.590 

.C0640 

9,700 

2.273 

4.625 

131 

131.197 

1022.698 

1153.895 

.00656 

9,516 

2.335 

4.750 

132 

132.202 

1021.998 

1154.200 

.00673 

9,276 

2.398 

4.878 

133 

133.207 

1021.293 

1154.505 

.00690 

9,046 

And  its  Appliances 


301 


TABLE  No  9. — CONTINUED. 

The  Properties  of  Water  from  32°  to  212°  Fahrenheit. 


ELASTIC  FORCE. 

lem- 
perature 
in  Fah- 
renheit 
Degrees. 

NUMBER  OF  BRITISH  THERMAL  UMTS  IN 
ONE  POU.VD  FROM  ZEKO  (FAHRENHEIT). 

Weight 
ox  One 
Cubic 
Foot  of 
Vapor 
iu 
Decimals 
of  a 
Pound. 

Number 
of 
Cubic 
Feet  of 
Steam 
from  One 
Cubic 
Footol 
^ater. 

In  Pounds 
on  the 

Square 
Inch. 

In  Inches 
of 
Mercury. 

Number 
of  Units  of 
Heat  in 
Water. 

Number  of 
Units  of  Heat 
Required  tor 
Evaporation, 
Called 
Latent  Heat 

Total 
Number  . 
of  Units  of 
Heat 
Contained 
'    in  Vapor. 

2.461 

5.009 

134 

134.212 

1020.598 

1154.810 

.00707 

8,826 

2.526 

5.143 

135 

135.217 

1019.898 

1155.115 

.00725 

8,611 

2.594 

5.280 

136 

136.222 

1019.198 

1155.420 

.00743 

8,401 

2.663 

5.420 

137 

137.227 

1018.498 

1155.725 

.00761 

8,191 

2.732 

5.563 

138 

138.223 

1017.797 

1156.030 

,00780 

7,991 

2.803 

5.709 

139 

139.239 

1017.096 

1156.335 

.00799 

7,798 

2.876 

5.858 

140 

140.245 

1016.395 

1156.640 

.00819 

7.613 

2.952 

6.011 

141 

141.251 

1015.694 

1156.945 

.00839 

7,433 

3.029 

6.167 

142 

142.257 

1014.993 

1157.250 

.00860 

7,258 

3.108 

6.327 

143 

143.263 

1014.292 

1157.555 

.00881 

7,088 

3.188 

6.490 

144 

144.269 

1013.591 

1157.860 

.00903 

6,920 

3.270 

6.657 

145 

145.275 

1012.890 

1158.165 

.00925 

6,755 

3.353 

6.827 

146 

146.281 

1012.189 

1158.470 

.00948 

6,595 

3.438 

7.001 

147 

147.287 

1011.488 

1158.775 

.00971 

6,440 

3.526 

7.179 

148 

148.293 

1010.787 

1159.080 

.00993 

6,290 

3.615 

7.361 

149 

149.299 

1010.086 

1159.385 

.01016 

6,144 

3.707 

7.547 

150 

150.305 

1009.385 

1159.690 

.01040 

6,004 

3.801 

7.736 

151 

151.311 

1008.684 

1159.995 

.01064 

5,867 

3.896 

7.929 

152 

152.318 

1007.982 

1160.300 

.01089 

5,734 

3.992 

8.127 

153 

153.325 

1007.280 

1160.605 

.01114 

5,604 

4.090 

8.329 

154 

154.332 

1006.578 

1160.910 

.01140 

5,477 

4.191 

8.535 

155 

155.339 

1005.876 

1161.215 

.01167 

5,353 

4.295 

8.745 

156 

156.346 

1005.174 

1161.520 

.01194 

5,232 

4.400 

8.959 

157 

157.353 

1004.472 

1161.825 

.01222 

5,114 

4.507 

9.178 

158 

158.360 

1003.770 

1162.1CO 

.01250 

5,000 

4.617 

9.401 

159 

159.367 

1003.068 

1162.435 

.01279 

4,888 

4.729 

9.629 

160 

160.374 

1002.366 

1162.740 

.01308 

4,779 

4.843 

9.861 

161 

161.381 

1001.664 

1  163.045 

..01338 

4,673 

4.960 

10.098 

162 

162.389 

1000.961 

1163.350 

.01368 

4,569 

5.079 

10.340 

163 

163.397 

1000.258 

1163.655 

.01399 

4,467 

5.200 

10.588 

164 

164.405 

999.555 

1163.960 

.01430 

4,368 

6.324 

10.840 

165 

165.413 

998.852 

1164.265 

.01462 

4,271 

5451 

11.097 

166 

166.421 

998.149 

1164.570 

.01495 

4,177 

5.580 

11.359 

167 

167.429 

997.446 

1164.875 

.01528 

4,085 

5.711 

11.627 

168 

168.437 

996.743 

1165.180 

.01562 

3,996 

5.845 

11.900 

169 

169.445 

996.040 

1165.485 

.01596 

3,910 

5.981 

12.178 

170 

170.453 

995.337 

1165.790 

.01631 

3,826 

6.120 

12.461 

171 

171.461 

994.634 

1166.095 

.01667 

3,744 

6.262 

12.750 

172 

172.470 

993.930 

1166.400 

.01704 

3,664 

6.408 

13.045 

173 

173.479 

993.226 

1166.705 

.01741 

3,586 

6.555 

13.345 

174 

174.488 

992  522 

1167.010 

..01779 

3,510 

6.704 

13.651 

175 

175.497 

991.818 

1167.315 

.01817 

3,436 

6.857 

13.963 

176 

176.506 

991.114 

1167.620 

.01855 

3,365 

7.013 

14.281 

177 

177.515 

990.410 

1167.925 

.01894 

3,295 

7.172 

14.605 

178 

178.524 

989.706 

1  168.230 

.01934 

3,226 

7.335 

14.935 

179 

179.533 

989.002 

1168.535 

.01975 

3,159 

7.500 

15.271 

180 

180.542 

988.298 

1168.840 

.02017 

3,093 

7.668 

15.614 

181 

181.551 

987.594 

1169.145 

.02060 

3,029 

7.841 

15.963 

182 

182.561 

986.889 

1169.450 

.02104 

2,966 

8.016 

16.318 

183 

183.571 

986.184 

1  169.755 

.02148 

2,905- 

8.194 

16.680 

184 

184.581 

985.479 

1170.060 

.02193 

2,846 

302 


Steam  Engine  Indicator 
TABLE  No.  9. — CONTINUED. 

The  Properties  of  Water  from  32°  to  212°  Fahrenheit. 


ELASTIC  FORCE. 

Tem- 

NUMBER OF  BRITISH  THERMAL  UNITS  IN 
ONE  POUND  FROM  ZERO  (FAHRENHEIT). 

Weight 
of  One 

PnHi/* 

Number 
•of 

OnKirt 

In  Pounds 
on  the 

In  Inches 
of 

perature 
in  Fah- 

Number 
Of  Units  of 

Number  of 
Units  of  Heat 
Required  for 

Total 
Number 
of  Units  of 

v/UDIC 

Foot  of 
Vapor 
in 

VllDlC 

Feet  of 
Steam 
from  One 

Souare 

renheit 

Heat  in 

Evaporation, 

Heat 

Decimals 

Cubic 

Mercury. 

Degrees. 

Called 

Contained 

of  a 

Foot  of 

Inch. 

Water. 

Latent  Heat. 

in  Vapor. 

Pound. 

Water; 

8.375 

17.049 

.    185 

185.591 

984.774 

1170.365 

.02238 

2.789 

8.558 

17.425 

186 

186.601 

984.069 

1170.670 

.02284 

2^33 

8.745 

17.807 

187 

187.611 

983.364 

1170.975 

.02331 

2,678 

8.936 

18.196 

188 

188.621 

982.659 

1171.280 

.02379 

2,624 

9.132 

•    18.593 

189 

189.632 

981.953 

1171.585 

.02428 

2,571 

9.330 

18.997 

190 

190.643 

981.247 

1171.890 

.02470 

2,519 

9.532 

19.408 

191 

191.654 

980.541 

1172.195 

.02529 

2,469 

9.738 

19.827 

192 

192.665 

979.835 

1172.500 

.02580 

2,420 

9.947 

20.253 

193 

193.676 

979.129 

1172.805 

.02632 

2,372 

10.160 

20.687 

194 

194.686 

978.424 

1173.110 

.02685 

2,325 

10.377 

21.129 

195 

195.697 

977.718 

1173.415 

.02740 

2,279 

10.597 

21.579 

196 

196.708 

977.012 

1173.720 

.02796 

2,234 

10.822 

22.036 

197 

197.719 

976.306 

1174.025 

.02853 

2,190 

11.051 

22.502 

198 

198.730 

975.600 

1174.330 

.02910 

2,147 

11.284 

22.976 

199 

199.741 

974.894 

1174.635 

.02967 

2,105 

11.521 

23.458 

200 

200.753 

974.187 

1174.940 

.03025 

2,064 

11.761 

23.948 

201 

201.765 

973.480 

1175.245 

.03083 

2,024 

12.006 

24.446 

202 

202.777 

972.773 

1175.550 

.031-12 

1,985 

12.255 

24.953 

203 

203.789 

972.066 

1175.855 

.03201 

1,953 

12.508 

25.468 

204 

204.801 

971.359 

1176.160 

.03261 

1,916 

12.766 

25.992 

205 

205.813 

970.653 

1176.465 

.03323 

1,880 

13.028 

26.525 

206 

206.825 

969.945 

1176.770 

.03386 

1,844 

13.295 

27.067 

207 

207.837 

969.238 

1177.075 

.03450 

1,809 

13.568 

27.619 

208 

208.849 

968.531 

1177.380 

.03516 

1,775 

13.843 

28.180 

209 

209.861 

967.824 

1177.685 

.03584 

1,741 

14.122 

28.751 

210 

210.874 

967.116 

1177.990 

.03654 

1,708 

14.406 

29.332 

211 

211.887 

966.408 

1178.295 

.03725 

1,676 

14.700 

29.9218 

212 

212.900 

965.700 

1178.600 

.03797 

1,644 

INIDKX. 


PAGE 

A 

Absolute  information  from  diagram,        -    79 
"         pressure,         -----    21 

Action  of  steam  in  cylinder,  theory  of      -  137 

"        "      "        ''  jacketed  cylinders,      -  141 

Actual  curves,        ------  105 

Adiabatic  curve,  -  -  •  ...  105 
Adjuster  for  indicator  cord,  -  -  31-72 
Admission  line,  ------  92 

"  "    late, 150 

"    correctness  of    -        -        -  148 
"    method  of  determining 

the  correctness  of,        149-151 
Amsler  polar  planimeter,    -        -        -        -  198 
"  mean  effective 

pressure  from,    198 

Application  of  indicator,  -  -  -  -  35 
Areas  and  circumferences  of  circles,  289 

Areas  of  large  circles,  finding  294 

Atmospheric  line,          -        ...        75-91 
"      tracing,  -        -        -    75 

Averager  for  measuring  diagrams,  -  -  185 
Available  power,  -----  221 

B 

Back  pressure,      ------     219 

"          cause  of  excessive,    -        -    219 
"          in  condensing  and  non- 
condensing  engines,        220-277 
"         loss  from,    -        -        -        -     219 

total 22 

"          line,  22-94 

Blanks,  example  of  printed,      -  78 

Boiler  pressure,    ------      21 

Boilers,  testing,    -  -    277 

c 

Calculating  water  consumption  by  con- 
stant,      165 

Care  and  use  of  indicator,  68 

Carrying  pulleys,          -  71 

Calorimeter  tests,  manner  of  making,    -  248 

"      rule  for  computing,     -  251 


PAGE 

Calorimeters,  different  kinds,  -        -        -  244 

Calorimeter,  description  of  barrel,          -  248 

Prof.  Carpenter's,        -        -  255 

Clearance,  .....     22-23-87 

"        estimating,                  ...  88 

"        percent.     -----  23. 

"       the  effect  of       -       -       -       -  219 

line, 87 

"           "    locating,     -       -       -        -  88 
Close  agreement  of  the  actual  with  the 

isothermal  in  jacketed  cylinders,  143 

Coffin  averager,            185 

"            "           construction  of,       -        -  186 
"             "           finding  the  mean  effect- 
ive pressure  with          -  188 
"             "           principle    of  operation 

of  the      -        -     '  -       190-197 

Compression,         -                                «        -  22 

"  and  clearance,      -        -        .219 

curve, 95 

Comparison  of  diagrams  from  throttling 

and  cut-off  engines,           -        -        -  201 
Comparison  of  results  between  large  and 

small  clearance,         -  227 
Condensing  engine  diagrams,          -      266-267 
Condensing  and  non-condensing    dia- 
grams compared,        -        ...  227 
Condensation  in  cylinders,        -        -        -  138 
loss  from       -        ...  142 
Condenser,  effect  of  addinj      -  214. 
"           pressure  in                        -        -  214 
Condensation  in  uujacketed  cylinders,  -  139 

Cock,  three  way 30 

"      section  of  three  way  31 

Cord,  indicator,             -----  72 

"      adjuster       ------  31 

"      stretching  of  the        -        -  72 

Computing  horse  power,    -        -        -        -  112 

Computing  steam  accounted  for  by  the 

indicator,  different  methods  of    152-157 
Combining  diagrams,  method  of    -       229-233 
from  compound 

engines,      -        -  228 


304 


Index. 


PAGE 

Compound   condensing-    engines,   dia- 
grams from,        ....      261-268 
Curves,  theoretical  or  isothermal    -        -      97 
"        agreement  of  actual  and  theo- 
retical expansion,       -        -        -     106 
Cut-off,  the  point  of    -        -        -        -       93-2*Z 
"        locating  the  point  of    -        -      108-111 
"        the  best  point  to     -        -       -       -    214 


Data  necessary,    ---.--      77 

"     how  to  preserve  77 

Description  of  indicator,    -       -       -        -      16 

Device,  indicator  testing,  -       -        -        -    175 

Diagrams,  indicator    -----      16 

''  the  information  to  be  derived 

from         ....         79-82 
"           from  Marsh  steam  pump,       -    274 
"           combining,         ....    228 
Diagram,  essential  ieatures  of  a  well- 
formed       84 

"  lines  and  points  of  the    -        -      91 

Diagrams,  to  take  sinmltanously    -        -      63 

"  the  outline  of    -        -        -  83 

engine  underloaded  -    117 

"  not  desirable      -        -        -        -    123 

reading  the        -  146 

Diagram  representing  the  economy  of 

high  pressure  -        -        -        -    ?n 

Diagram  showing  the  most   favorable 

point  of  cut-off           -  216 
Diagram  from  a  steam  jacketed  cylin- 
der,        143 

Diagrams  from  both  ends  of  a  cylinder,  85 
Diagram,  good  features  of  a  -  -  -  80 
Diagrams,  measuring  a  large  number  of  185 
Diagram,  mmes  of  the  lines  of  the  91-95 

Diagrams,  study  of 83 

method  of  taking  75 

from  pumps,    -  272-273 

Diagram  averager  .     185 

Diagrams  from  various  engines,      -      258-267 

Diagrams  to  show  the  effect  between 

large  and  small  clearance,      -      219  226 
Diagrams  from    fteam    cylinder    and 

ammonia  compressor,       -        -      239-240 

Diagrams  from  gas  engines,      -        -        -    241 

"  from  oil  engines,      ...    242 

miscellaneous,          -        -      258-267 

"Directions  for  indicating,          -        -        -      75 

Driving  gear  for  indicator,  54 

Drum  motion,  testing  accuracy  of  -  52 

Drum  stop  motion,     -  €1-62 

Drum  spring,        .-----      74 


PAGE 

Economy  in  the  use  of  steam    ...  282 

of  expansion,      -        •        123-125-208 

"  heating  feed  water,      -        -  284 

"  high  pressure,       ...  209 

steam  engine      ....  275 

Engines,  testing           .....  282 

"         compound    -----  267 

"         comparison  of  diagrams  from 

throttling  and  cut-off      -      202-207 

Essential  features  of  diagrams,        -        -  84 

Exhaust-closure,          .....  94 

Exhaust-closure,  early  and  late,      -        -  219 

Exhaust,  heat  lost  at           -        -        -        -  210 

Exhaust-line, 93 

Exhaust-valve,  leaky          ....  148 

Expansion  of  steam,           -  119 

"           line  or  curve,                             -  93 

ratio  of      -        -  130 

"           initial        -  22 

"           curve,  peculiarities  of     -  83 

line,  and  leaky  valves,   -        -  147 

"  curve,  agreement  of  actual 

and  theoretical  -      143-145 

curve,  geometrical  method 

of  finding  points  in  the      -  101 
Experiments  to    determine    the    most 

favorable  point  of  cut-oft",        -        -  215 


Feed-water,  economy  of  heating      -        -  284 
Feed-water  accounted  for  by  the  indi- 
cator,           ......  152 

Footpound,           -        -        -        •        -        -112 
Fricaon,  effects  of        -                                 -  179 
"         of  indicator  piston      -        -        -  181 
"          "         "               "      how  to  de- 
termine        182 


Gases,  Mariotte  law  concerning  -        -      97 

Gas*  engines,  diagrams  from     -  -      240-241 

Gauge  or  boiler  pressure,  21 

Guide  or  carrying  pulleys,          -  71 

Guide  pulleys,  disadvantages  of  -        -      71 

Gas  and  oil  engine  diagrams    -  234 


Heat  lost, -        -  214 

"      available     -        -        -                -        -  210 

"      latent           ......  20 

"      lost  at  exhaust  -----  210 

"      sensible        ------  20 

"      the  unit  of  -        -----  20 


Index. 


305 


PAGB 

Heat  units             ......  20 

High  pressure,  economy  ef       -       -       -  209 
High  speed    diagram  compared    with 

moderate  speed,          ...      267-268 
High  speed  engines,  manner  cf  using 

the  cord  ou          -----  51 

Holes  in  cylinder,   position    for    indi- 
cator,      36-37 

Hooking  the  cords,      -----  51 

Horse  power,  elements  of          ...  112 

"        finding  the  -        -                -  112 
"        for    one    pound    mean 

effective  pressure,    -        -  113 

"            "        indicated       -                -       -  21 

"            "        net          -----  21 

41            "        factors  for     -  113 

41            "        byordinates         -        -        -  114 

Hyperbolic  logarithms,       -        ...  128 

curve           -----  97 

"           logarithms,  table  of        -       -  129 


Indicator,  brief  history  of  the  n 

Watts'  original  -        -         -       n 

"         construction  of    n 
"  McNaught  12 

description  of         -       13 
"  parts  of        -        -        -        -  14 

"  size  of  piston  of        -        -        -      14 

"  purpose  of the  16 

"  care  required  in  the  use  of     -      68 

Tabor  ....          24.25 

"  construction  of  parts  of    -         24-30 

oiling  the    -  68-183 

"  scales  ....         73-87 

springs        ....    32-33-34 
to  use  ...      73 

appliances,  cuts  of   -        -         44-53 
"  electrical  appliance  -      65 

testing  devise,          ...    j-§ 
"        construction  of    176 
manner  of  using  176 
information  de- 
rived from      -    180 
reducing  gear,  ...      54 

parts  of     -         55-57 
"     directions  for 

using       -         58-60 

"  cord 72 

1    adjuster  31 
driving  gear       ...        -      54 
"           how  to  attach  the  75 
piston,  the  effects  of  momen- 
tum of 181 


PAGE 

Indicators,  using  one  or  two     -       -        30-77 

Indicator  diagrams,  the  production  of     17-86 

"         explanation  of    17-18-19 

"         cylinder,  warming  up  -      75 

"         card,  proportionate  length  of        38 

"          diagrams  from  various  engines  257 

"         piston,    effects   of    a    tightly 

fitting  .    182 

Initial  expansion,       -        ....      95 

Initial  pressure,  ....       92-213 

Isothermal  curve^  97 

"        locating  points  on  the    98 

"        geometrical  method  for 

constructing  the          101 


Jacketing,  cylinder, 


-    143 


Latent  heat,  -  -  -  20 

Lazy  tongs,  39~4<> 

"          "        proportion  of  -  -        40-41-42 

Leakage  .    -  -      79 

Leaky  Valves,  detecting  by  the  indicator   106 
Length  of  diagrams,  -  -  38 

Levers,  reducing       -  46-49 

Locating  clearance  line  on  diagram,         88 
"          point  of  cut-off   -  -         io8-nr 

Long  indicator  pipes,  -  -  -      37 

M 

Management  and  care  of  indicator,         -      6$ 

Mariotte  law  of  gases,         -  -  -      97 

Manner  of  taking  diagrams,         -  -      75 

Marsh  steam  pump  diagrams^       -  -    274 

Mean  effective  pressure,      -  -  22~95 

computing         -    117 

"  "  "          measuring  by 

ordinates  the        114 
Mean  effective  pressure,    horse  power 

for  oue  pound,  -  -  -    113 

Mean  pressure  of  expanding  steam,  the 

rule  for  finding  the    -  -         130-131 

Measuring  diagrams,  -          -  -    114 

Memoranda  of  diagrams,  making  -      77 

Method  of  indicating  a  steam  engine     -      75 

''        "  computing  horse  power,       113-114 

Moisture  in  steam,     -  244 

Motion,  Watts'  parallel       -  -  -      14 

straight  line  -  -  -IS 

drum  -  16-70 

Movement  of  pencil,  -  -      16 


306 


Index. 


0 


PAGE 


Oilengines,  operation  of    -  -    243 

Oil  engine  diagrams, 
Oiling  the  indicator, 

Ordinates,  horse  power  by  -    _       -     114 

"  different  methods  of  measur- 

ing the  -    .     "6-ii? 


-  i6- 
44-45" 

-  45 


-  15 
69-70 
25-36 
47-4Q 

-  184 
198 

184 
93-213 
'  ,93 

21-22 

-  219 

21 
21 

22-95 


Paper-drum, 
Pautagraph 

11  adjusting  the  - 

Paral'el  motion,  Watts 
Parallel  or  straight  line  motion,    - 
Pencil,  adjusting  the 
Pencil  movement,  proportioning  of 
Pendulum  reducing  gear,    - 
Piping  for  indicators, 
Planimeters, 

"  Amsler  polar 

Planimeter.  measuring  mean   effective 

pr-ssure  by  the 
Point  of  cut-off, 

"      "  exhaust, 
Pressure,  ab-olute      - 

"       "  back'  -  - 

"          boiler 

"         initial 

«•          mean  effective      - 

"          of  expanding  steam 

'•          of  expanding  steam,   rule   for 

finding  the      __    - 
"         terminal     - 

••         total  back  .  -      22 

"          ior  indicator  springs 
Priming,  extent  of  -    244 

Printed  blanks, 

Pulleys,  carrying        -  -      ?*• 

Pump  diagrams,         -    '  •         272-273 


Ratio  of  expansion, 

Reducing  levers,        -  -      47 

Reducing  gears,  different  kinds  of  5  '-53 

Re-evaporation, 

Resistance  to  motion  of  th  -  pistou  of  a 

steim  engine. 
Rule  for  finding  the  mea:i   pressure  of 

expanding  steam,         -  -        J33  131 


Safe  pressure  for  indicator  springs, 
Satuiated  steam, 


73 


Scales,  indicator        -  -      73, 

Sensible  heat,  -      20. 

Serrated  lines  of  the  diagram,       -  -    181. 

Specific  heat,  -      20 

Springs,  how  marked,          -  73 

Spring  to  use,  proper  -      7^ 

Springfield  gas.engine  diagrams,   _  2^7-2  38 

Steam,  dry       -  -21 

"         expansion  of                         -  -.     119 

li  le                   -           -           -  f    -      92 

"        exhau  ted  per  hour,  -     152 

"        line,  straight  ...    209 

"        per  horse  power  per  hour  -     152 

*'        jacketed   cylinders(   diagrams 

from  -    14} 

"        pressure  of  expanding       -  -     123 

14        pipe,  large  and  small,        -  -      79 
*'        pressure,  working   with   hi^h 

and  low, 

"        properties  of  saturated 

"        saved  in  clearance,  -     i3) 

"        i-uperheated,        •                  -  -      2c 

"        or  water  consumption,       ~  -      2\ 

''        admission  of  -      84 

"        connections  for  indicators,  -      31 

"         i:i  cylinders,  (actio  •  of)     -  -     i  ;? 
"        accounted  for  by  the  indicator,  -     152 

"        valve,  leaky               -           -  ?9 


Tabor  indicator,        -  24  25 

"  "          with   reducing  motion 

and  parts,          -  51  57 

•i  "          with   electrical  attach- 

ment      -  -  65 

»  "         with  comb.  ned  pistons,      2,5 

Table  of  hyperbole  logarithms      -  -     12^ 

"       showing  the  theoretical  ecouomy 

of  using  steam  expansively,          -    132 
«'       of  constant-i  for  fin  ling  the  average 
pressure     with     any     pressure    of 
steam,  -     1  34- 

"  of  average  pressure  of  steam  in  the 
cylinder  with  different  rates  of 
expansion,  -  -  .  -  .  -  J35 

"       quantity  of  steam  accounted  for  by 

the  indicator,  -         170-171 

"       sh  nving  saving  effected  by  the  use 

of  feed-water  heateis,         -  -     286 

"       aieas  and  circumferences  of  circles  2^9 

properties  of  snturated  steam,        -     295 

properties  of  water.  -    299 

Te*nnical  te«-rn^  :o  2I--22-2} 

Ter.ainal  pressure,  •    55-147-  275 


Index. 


307 


Terminal  pressure,  cause  of  high 
theoretical    - 
Tests,  different  methods  of  making 


PAGE 

-  147 

-  14? 

-  277 


,'hat  should  be  noted  in  making,     277 


Testing  engines  and  boilers, 
Theoretical  curve,  object  of  drawing  the 
points  from  which  to 

draw  the 

"        reasons  for  establish- 
ing the 
Theoretical  diag-am, 


2/9 


economy  of  expansion, 
Three-way  cock, 


98 

-  103 

-  120 
I  26-- 1 .33 

-  3° 


Underloaded  engines,  -  •  116-212 

Unit  of  heat,  -  -  -  .20 

"  work,  -  20 

Uses  to  which  the  indicator  may  be 

applied,            -          -  -          .      -IP 


Vacuum-line,  establishing              •  -  87 

Valves,  adjusting       -            .            .  -  80 

detecting  leaky       -           .  "79 

Valve  lap,         -  23 

"    lead,   '    -           -           »           -  23 

"    gear,  incorrect,           -  -  82 

w 

Watts' original  indicator,    ~         -.  -  n 

parallel  motion,       -  -14 
Water  consumption,  making  allowance 

for           -                      -           -  -  164 

"        per  horse  power  per  hour  -  152 

Wiredrawing             -           -          .i  .  23 

Work  and  heat           -           •  »  210 

"    in  the  two  ends  of  the  cylinder  •  83* 

"    the  unit  of                    -           -  -  20 


Zero  line,         -          •          «          •          -     86 


ADVERTISEMENTS. 


THE  IMPROVED  TABOR  STEAM  ENGINE  INDICATOR 

With  Outside  Spring. 


With  HoughtalitiK  Reducing:  motion. 

Coffin  Averagers,  Amsler  Plauimeters,  Pantographs,  Lazy  Tongs,  Ashcroft 
Reducing  Wheels,  Three  Way  Cocks,  Carrying  Pulleys,  Etc. 

.•\\vurded    Grand    Prize    at    World's    Fair,    St.    Louis,    1004. 

THE  ASHCROFT  MANUFACTURING  CO., 

SOLE    MANUFACTURERS, 

85-87-89  LIBERTY  STREET,  22-24-26  S.  CANAL  STREET, 

NEW  YORK  CHICAGO. 


EDSOIN 


Pressure  Recording  and  Alarm  Gauge 


For 

Steam, 

Air, 

Gas, 

Water, 


Ammonia 

or 

any 

Fluid 

Pressure. 


STYLE  No.  1. 
Awarded  Grand  Prize  at  World's  Fair,  St.  Louis,   1904. 

THE  ASHCROFT  MANUFACTURING  CO. 

SOLE  MANUFACTURERS. 


85-87-89   LIBERTY  ST., 
NEW  YORK. 


22-24-26  8.  CANAL  ST., 
CHICAGO. 


Consolidated 
Nickel  Seated 
Pop  Safety  Valve. 


Water 
Relief 
Valves. 


Cylinder 

Relief 

Valves. 


Awarded  Gold  Medal  at  World's  Fair,  St.  Louis,   1904. 

The  Consolidated  Safety  Valve  Co 


SOI.  1C 

85-87-89  Liberty  St.,          22-24-26  S.  Canal  St., 
New  York.  Chicago. 


The  Metropolitan  Automatic  Injector 


Especially  adapted  for  Hoisting  Engines,  and  for 

service  where  an  Injector  operated  entirely 

by   one   handle   is   required. 


H-D  EJECTORS,    ..... 
;        H-D  WATER  HEATERS,  Etc. 

Awarded   Gold    Medal    at    World's    Fair,    St.    Kouis,    1904. 

THE  HAYDEN  &  DERBY  MFG.  CO., 

SOLE   MANUFACTURERS. 

85-87-89  Liberty  St.,  22-24-26  S.  Canal  St., 

New  York.  Chicago. 


THE  HANCOCK  INSPIRATOR 

STATIONARY   TYPE. 


For  Stationary  and  Portable  Boilers. 

BEWARE  OF  IMITATIONS,  and  for  your  own  protection   see  that  the 
Inspirator  is  marked  "The  Hancock  Inspirator  Co." 

HANCOCK  EJECTORS,  HANCOCK  COMPOSITE  TYPE  INSPIRATORS,  &o. 

Awarded  Gold  Medal  at  World's  Fair,  St.  Louis,   1904. 

THE   HANCOCK  INSPIRATOR  CO., 

SOLE    MANUFACTURERS. 

85-87-89    Liberty   St.,  22-24-26    S.    Canal   St., 

New  York.  Chicago. 


The   Hancock  Valve 

MADE   IN 

GLOBE,  ANGLE,  SIXTY  DEGREE  and  CROSS. 


For  high  pressure  steam, 
For  superheated  steam, 
For  hot  water, 
For  Blow-off, 

For  severe  conditions  gen- 
erally. 


HANCOCK  CHECK  VALVES 

HANCOCK  BLOW-OFF  VALVES,  &c. 

Awarded  Gold  Medal  at  World's  Fair,  St.  Louis,   1904. 

THE  HANCOCK  INSPIRATOR  CO., 

SOLE  MANUFACTURERS. 

85-87-89  Liberty  St.,         22-24-26  S.  Canal  St., 
New  York.  Chicago. 


Manning, 
Maxwell  & 


incorporated, 


Railway  and  Machinists' 
Tools  and  Supplies. 

85-87-89  Liberty  Street,  New  York. 


Branch  Offices: 

22-24-26  S.  Canal  Street,  Chicago,  111. 
721  Arch  Street,  Philadelphia,  Pa. 
1  28  Oliver  Street,  Boston,  Mass. 
Park  Building,  Pittsburg,  Pa. 
Williamson  Building,  Cleveland,  O. 
Frisco  Building,  St.  Louis,  Mo. 
Woodward  Building,  Birmingham,  Ala. 
Kirk  Building,  Syracuse,  N.  Y. 


THE  SHAW  ELECTRIC  TRAVELING  CRANE. 


Sixty  ton  Electric  Traveling  Crane,  Subway  Station,  Interborough   Rapid 
Transit  Company,  New  York  City. 

For    the    Machine    Shop,    the    Power 
House,  the  Foundry,  the  Steam  Plant. 

Awarded   Grand  Prize   at   the   World's   Fair,  .St.    Louis,    19O4* 

THE  SHAW  ELECTRIC  CRANE  CO., 

SOLE   MANUFACTURERS, 

85-87-89  LIBERTY  STREET,     -     NEW  YORK. 


BRANCH    OFFICES: 
22-24-26  S.  Canal  St.,  Chicago,  HI.          Williamson  Building,  Cleveland,  O. 


721  Arch  St.,  Philadelphia,  Pa. 
128  Oliver  St.,  Boston,  Mass. 
Park  Building,  Pittsburg,  Pa. 


Frisco  Building,  St.  Louis,  Mo. 
Woodward  Bldg.,  Birmingham,  Ala. 
Kirk  Building,  Syracuse,  N.  Y. 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 
This  book  is  DUE  on  the  last  date  stamped  below. 

Fine  schedule:  25  cents  on  first  day  overdue 

50  cents  on  fourth  day  overdue 
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ENGINEERING  LIERARY 


DEC  5    1950  ; 
DEC  1  5  1950^- 


LD  21-100m-12,'46(A2012sl6)4120 


THE  UNIVERSITY  OF  CALIFORNIA  UBRARY 


